Sample Final Solutions: 1) x2 9 x dx : Trig sub: Let x 3sec . Thus dx 3 sec tan d , x 2 9 (3 sec ) 2 9 9 tan 2 3 tan a) x2 9 3 tan (3 sec tan ) dx d 3 (tan 2 )d 3 (sec 2 1)d 3[tan ] c x 3 sec bnbbNow make a triangle using 3[sec tan ] c x2 9 x sec 1 c 3 3 1 1 x dx ( (1 cos 2 x)) 2 dx 1 2 cos 2 x cos 2 2 x)dx 2 4 1 1 3 1 1 (1 2 cos2 x cos 4 x)dx x sin 2 x sin 4 x c 2 2 8 4 32 b) Use double angle twice: 1 4 x sec 3 sin 4 7x2 x 9 dx : x3 x 7x 2 x 9 2x 1 9 dx ( 2 )dx . c) Partial fractions will give (see below for details) 3 x x x 1 x 7x2 x 9 dx ln( x 2 1) tan 1 x 9 ln x c Separate the first fraction and use u-sub for the first part. x3 x 7 x 2 x 9 Ax B C 2 7 x 2 x 9 x( Ax B) C ( x 2 1) . First (For the partial fractions, 2 x( x 1) x 1 x let x=0. We get C = 9. 7 x 2 x 9 x( Ax B) 9( x 2 1) ( A 9) x 2 Bx 9 . By equating coefficients, we get A = -2, B=1. u (ln x) 2 dv dx du d) Use parts twice: x(ln x) 2 2 ln x dx : ln xdx x ln x Use parts for ln xdx : 2 ln x dx, v x : x apply the parts formula to obtain u ln x, dv dx du 1 xdx x ln x 1dx x ln x x . x Therefore, 1 dx, v x . x (ln x) 2 dx x(ln x) 2 2 ln x dx x(ln x)2 2( x ln x x) c . a) e) e 3x cos 4 xdx : the integral. Use the circle method: Use parts twice. We can make a table to summarize U Dv e 3e 3 x cos 4x sin 4 x 4 9e 3 x Ax 3x f) e3 x sin 4 x 3 3 x 9 e cos 4 x e3 x cos 4 xdx . 4 16 16 16 1 3 e 3 x cos 4 xdx ( e 3 x sin 4 x e 3 x cos 4 x) c 25 4 16 e3 x cos 4 xdx sec 3 Solving for e 3x cos 4 xdx , x tan 3 x dx sec 2 x tan 2 x(sec x tan x)dx sec 2 x(sec 2 x 1) sec x tan xdx . Let u sec x du sec x tan xdx . u5 u3 (sec 5 x) (sec 3 x) c c 5 3 5 3 1 1 dx dx : Complete the square first, then use trig sub: x 2 4x 5 x 2 4x 5 sec 2 x(sec 2 x 1) sec x tan xdx u 2 (u 2 1)du g) 1 ( x 2) 2 1 dx . x 2 tan dx sec 2 d . We have ( x 2) 2 1 tan 2 1 sec . Therefore 1 1 2 2 x 2 4x 5 dx sec sec d sec d ln sec tan c ln x 4x 5 ( x 2) c 1 1 1 2 2 2 h) Use two double angle formulas: sin x cos x sin 2 x to write (sin x cos x ) ( sin 2 x ) sin 2 x and 2 2 4 1 sin 2 2 x (1 cos 2 x) We have 2 1 1 4 2 2 2 2 2 sin xdx cos xdx sin x cos x sin xdx m : double angle 4 sin 2 x( 2 (1 cos 2 x))dx = 1 1 1 1 sin 2 2 xdx sin 2 2 x cos 2 xdx (1 cos 4 x)dx u 2 du (for the second integral, let 8 8 16 16 1 1 1 1 u sin 2 x du cos 2 xdx )= x sin 4 x sin 3 2 x c 2 16 64 48 x 1 dx : first u-sub. Write 1 x 4 as 1 ( x 2 ) 2 and let u x 2 du xdx . i) 4 2 1 x x 1 1 1 1 1 1 2 1 x 4 dx 2 1 u 2 du 2 sin u c 2 sin x c 1 3 2 2 3 x2 3 x2 2 x u j) x e dx : u x du 2 xdx du xdx . Separate x x x , x e dx x e xdx ue du 2 Next let u U Dv 1 eu 0 eu = ue eu u eu c x 2e x e x c 2 2 2) First observe that they are sequences, not series. a) Multiply the top and bottom by the conjugate: n 1 n lim n 1 n n 1 n 1 0 n 1 n n 1 n n! n n 1 n 2 2 1 1 n n 1 n 2 2 b) 0 lim n lim lim 0 ( the expression can be dropped n n n n n n n n n n n n n n n! 1 n! n! since it is less than 1) . Using the squeeze theorem, 0 lim n lim 0 lim n 0 lim n 0 n n n n n n n n 1 sin n 1 1 1 c) We know that 1 sin n 1 . Thus and lim ( ) 0, lim 0 . Thus by the squeeze n n n n n n n sin n theorem, lim 0 n n lim n n lim n 3) a) Use the ratio test: the ratio is 1 , thus convergent 3 (n 2 1) n 1 1 2 2n n n n 0 n 0 b) The root test fails. Next try TOD. n Apply the test of divergence using 1 n ) , take ln of both sides and bring down the exponent to get n2 1 2 ( 3 ) 1 1 n ln( 1 2 ) 1 2 1 n 1 n lim n lim ln(( 1 2 )) lim lim 0 . Since ln y 0 , y converges to n n n n 1 1 n 2 n(1 2 ) 2 n n n L’hopistal” : To compute lim (1 n e0 1. c) Thus the series is divergent by the test of divergence. 1 (ln 2) n 2 n : Use geometric series test: r 1 1. ln 2 d)Convergent by the comparison test: recall that Thus the series is divergent. ln n n c for any power of c. Pick any c that makes the 1 exponent of n greater than 1. ln n n2 1 n2 2 n n 2 2 2 1 n 3 2 1 and n e) Use the comparison test: guess is convergent since 3 2 is convergent by the p-test. n 1 3 n n n 1 behaves like n and p=2. Thus you construct a larger p-series by making the top bigger, the bottom smaller. the series is convergent by the comparison test. f) Use the integral test. Let 1 u ln x du dx . x divergent by the integral test. Then 2 1 x ln x dx lim n 1 nn 1 4 2 3 3 n 1 n n n3 2 b u b ln 2 1 2 du lim 2 u b b ln 2 . Thus , g) To use the comparison test, you must first take the absolute value since the test requires the terms to cos 4n be positive. Then use the theorem that states absolute convergence is convergence. 1 2 n 2 n h) is convergent by the p-test. Thus cos 4n 2 n n n2 is convergent. Therefore 1 n2 and n n cos 4n is convergent. 2 n2 n n 2 2n 2 n is convergent by the geometric series test. Therefore ( ) n n n 03 5 n 03 3 5 2n 2n 2 ( )n n n n 3 5 5 5 and is convergent by the comparison test. i) Apply the ration test: a n 1 1 3 5 (2n 1)( 2n 1) 1 3 5 (2n 1) lim n 1 4 7 (3n 2)(3n 1) n a 1 4 7 (3n 2) n lim 2n 1 2 1 3 5(2n 1)( 2n 1) 1 4 7 (3n 2) 1. lim n 1 3 5(2n 1) 1 4 7 (3n 2)(3n 1) n 3n 1 3 lim Thus the series is convergent by the ratio test. j) Since ln(n) grows very slowly, 1 (ln n) n 2 2 would diverge. Use the fact that ln n n any power for large n. . So use any power less than 0.5 (using a power more than 0.5 would make the series too small). ln n n 1 1 1 2 2 (ln n) n ( n) and 1 n 2 n is divergent by the p-test. Thus 1 (ln n) n 2 2 is divergent by the comparison test. k) cos 4 x cos 6 xdx : Use the product to sum formula: Since cos( A B) cos A cos B sin A sin B, cos( A B) cos As cos B sin A sin B , 1 1 cos A cos B [cos( A B) cos( A B)] cos 4 x cos 6 x [cos 2 x cos 10 x] . Thus 2 2 1 1 1 1 cos 4 x cos 6 xdx 2 (cos 2 x cos 10 x)dx 2 [ 2 sin 2 x 10 sin 10 x] c 4) tan 1 x , then replace x by 3x 2 . (1) n x 2 n1 2 n n 2n ( x ) dx (1) x dx c 2n 1 n 0 n 0 n 0 a) First find the power series expansion of tan 1 x 1 dx 1 x2 We have By evaluating the expression at x (1) n (3x 2 ) 2 n1 (1) n 32 n1 4 n2 x 2n 1 2n 1 n 0 n 0 b) First find the power series expansion for ln( 1 x) . Then use the box principle to replace x 1 1 (1) n x n and ln( 1 x) can be obtained by integrating that . 1 x 1 x n 0 = 0, we get c = 0. Thus ln( 1 x) 1 dx 1 x tan 1 (3x 2 ) n 0 Let x = 0 : ln( 1 x) (1) n ln( 1 x 2 ) (1) n n 0 (1) n x n dx x n dx (1) n n 0 2n 2 x n 1 n 0 n 0 x n1 c ln1 c c 0 n 1 x n1 c. n 1 x2. Next find c: Thus by ln( 1 x) (1) n n 0 x n1 . n 1 Therefore, Recall c) First observe that d2 1 2 1 1 d2 1 ( ) ( ). 2 3 3 2 dx 1 x (1 x) (1 x ) 2 dx 1 x 1 1 d2 1 1 d2 ( ) (1 x)3 2 dx 2 1 x 2 dx 2 1 n(n 1) x n1 2 n 0 1 x n(n 1) x n2 . 2 n 0 n 0 Thus n Therefore, x3 1 3 x n(n 1) x n2 3 2 n 0 (1 x) 5) a) This is separable. First separate x and y. Then integrate both sides. dy e 2 x y ye y dy e 2 x dx . dx y U Y Integrate the left hand side using parts: Dv ey e y ey 1 0 ye y e y 1 2x e c (this is an implicit solution) 2 dy xy 2 y 2 x 1 separable: first fact xy 2 y 2 x 1 ( y 2 1)( x 1) ( y 1)( y 1)( x 1) . dx dy dy xy 2 y 2 x 1 ( x 1)dx . But using partial fractions, dx ( y 1)( y 1) dy dy 1 1 1 1 [ ] . Thus xy 2 y 2 x 1 ( x 1)dx = ( y 1)( y 1) 2 y 1 y 1 dx ( y 1)( y 1) 1 1 1 1 x2 ( )dy ( x 1)dx ln ( y 1)( y 1) c 2 y 1 y 1 2 2 b) Thus 6) a) First find the points of intersection by solving 3 sin 1 sin find the area in the first quadrant: then double it. From crosses only 3sin . From Therefore, area = 6 to 0 to 5 6 , 6 . a)Use symmetry: , a typical line through the origin 6 , a typical line through the origin crosses only 1 sin . 2 1 2 [ 6 (3 sin ) 2 d 2 (1 sin ) 2 d ] 2 0 6 b) A typical line through the origin crosses enter the region through 3sin . Area = c) First set r = 0: 1 sin an d exits through 5 6 1 2 2 [(3 sin ) (1 sin ) ]d 2 6 1 2 sin 0 7 11 , 6 6 11 . 1 6 2 7 [((1 2 sin ) ]d 2 6 7) a) Need to find the length and the depth of the typical horizontal strip. Place the diameter of the sphere on the x-axis. Take a typical horizontal piece . Its length is is (length)(de pth) y (2 x)(9 y)y . circle of radius 5, x 2 y 2 25 x 25 y 2 (no need to use (2 x)(5 y)y (2 25 y 2 )(9 y)y . to 5, 2 25 y 2 (9 y)dy 5 Thus its Riemann sum Next express x as a function of y. Since (x,y) lie on the Thus 5 2x, its depth is 9 y . As since x is place on the positive side). y 0 , since the typical piece moves from -5 b) Place the bottom of the triangle on the x-axis. Take the typical horizontal piece. Its length is Using the famous Riemann sum is 2 1 3 triangle, we know the height of the triangle is 2 3 . (length)(de pth) y (2 x)((3 2 3) y)y . 2x, Thus the Next express x as a function of y. Find an equation of the line through (0,0) and (2, 2 3) . Using Math 50, an equation y y is y 3 x x Thus (2 x)((3 2 3 y )y (2 )(3 2 3 y)y . As y 0 , 3 3 2 3 2 since the typical piece moves from 0 to 2 3 , y(3 2 3 y)dy 0 3 8) Washer : use dx since you pick a typical piece perpendicular to the rotating axis. In washer you need to find the outer radius and inner radius. 1 [(2 ( x)) 2 (2 x) 2 ]dx 0 Shell: In shell, you need to find a) shell radius b) shell height use dy since a typical piece is taken parallel to the rotating axis. You need to break up the region into two sections since the left equation changes at y = 0. Also since you are using dy, you must solve the equations for x. 1 0 0 1 2 [ (2 y)(1 y)dy [(2 y)(1 ( y))dy] 9) a) mmn (x 2 ) 62.4x 2 y . The weight (force) of the typical piece is (volume)(density) = to express x as a function of y: weight is As Use similar triangles x 9 y x . (or an equation through (0,0) and (9,18) Thus the y 18 2 y2 (62.4)( )( )y 15.6y 2 y . 4 The distance is 18-y. Thus Work 15.6)( )( y 2 )(18 y)y. 8 y 0 W 15.6 y 2 (18 y)dy 0 (x 2 ) 62.4x 2 y . (62.4)( )(100 y 2 )y . c) The weight (force) of the typical piece is (volume)(density) = equation x y 100 x 100 y 2 2 is 5-y. Thus Work 2 2 Thus the weight is (62.4)( )(100 y 2 )(5 y)y. d) First find the spring constant k: As F kx 3 2k k Use the circle The distance 10 y 0 W 62.4 (100 y 2 )(5 y)dy 10 3 . 2 Then Work = b a kxdx 3 4 xdx 24 J 2 0 10) a) Apply the ratio test: lim n a n 1 an (3x 1) n 1 (3x 1) n1 2n 2 1 2(n 1) 2 1 lim lim n n (3 x 1) n (3x 1) n 2(n 1) 2 1 2n 2 1 2n 2 1 2n 2 1 ( 3 x 1 ) lim 3x 1 . n 2n 2 4n 3 n 2n 2 4n 3 ( 3x 1 ) lim 2 3x 1 1 1 3x 1 1 x 0 . 3 Now set this less than 1 and solve for x: 1 (3x 1) n 2 2 n 1 2n 1 n 1 2n 1 Now test the end points: first x=0. . This is convergent using the comparison test: 1 2n 1 2 1 2n 2 and 1 2n 2 is convergent by the p-test. (3x 1) n (1) n . 2 2 n 1 2n 1 n 1 2n 1 Next at x=-2/3: 2n n 1 1 2 1 is convergent. Thus the interval of convergent is b) Apply the ratio test: lim n a n 1 an (2 x 5) n n! n 1 f ( x) 2 [ ,0] 3 (2 x 1) n 1 1 (2 x 1) n1 (n)! (n 1)! 0 1. lim lim 2 x 5 lim n n 1 n ( 2 x 5) n n ( 2 x 5) n ( n 1)! n! Thus the radius of 11) ) This is convergent absolutely since we just showed that is , the interval is (, ) 1 2 8 48 f ' ( x) , f " ( x) , f ( 3) ( x ) 2 3 1 2x (1 2 x) (1 2 x) (1 2 x) 4 1 2 8 . Thus the second degree Taylor polynomial is f (2) , f ' (2) , f " (2) 5 25 125 1 1 4 ( x 2) ( x 2) 2 . For the error, the maximum f ( 3) ( x ) for 1.9 x 2.2 is attained when 5 25 125 48 x=1.9. M . Also, the maximum distance from a=2 for 1.9 x 2.2 is 0.2. Thus 4 .8 4 48 4 error 4.8 (0.2) 3 3! Thus at a=2, 12) a) Memorize 3n x n 2 n! n 0 xn e n 0 n! x , radius is . Substitute 3x into x, then multiply by x 2 f ( x) x e 2 3x (3x) n x n! n 0 2 b) Use the double angle formula. f ( x) sin 2 2 x (1) n x 2 n (2n)! . Thus n 0 1 (1) n (2) 2 n1 ( x) 2 n (the first term 2 n1 (2n)! 1 (1 cos 2 x) . 2 Use cos x 1 1 (1) n (2 x) 2 n 1 1 (1) n (2) 2 n ( x) 2 n 1 1 cos 2 x 2 2 2 2 n0 (2n)! 2 2 n0 (2n)! 1 1 1 of the summation is . Thus the term cancels with , so cancels. The radius is . 2 2 2 1 1 1 1 x2 2 (1 ) . Use the binomial formula c) Observe that f ( x) 9 9 x2 x2 3 9 ( 1 9 1 1 k n 1 x2 2 x 2n x 2 k (1 x) x . (1 ) 2 n , 1 x 3 so radius is 3. 3 9 9 9 n 0 n 0 n n 13) a) x 2 sin t , y 2 cos t ,0 t 2 d) Eliminate t using the identity a) Range: sec 2 t tan 2 t 1 x 2 y 2 1 . This is a hyperbola crossing the x-axis. x sec t , t x 1 . y tan t t y , y takes on all real 2 2 2 2 numbers. Direction: c) dx sec t tan t dt x t , y t 2 1. A) Range: Since : dy dx can be positive or negative. sec 2 t 0 . dt dt x t , t x t ( x) 2 x 2 . x t , so x is never y x4 1 positive. Thus Thus y is decreasing. y t 2 1 ( x 2 ) 2 1 x 4 1. y t 2 1 y 1 , Thus the graph is only the left side of I B) direction: since dx 1 dy dy 0 , it is traced to the left. 2t , t 0 0. dt dt dt 2 t increasing. 14) ) a) This is an improper integral: 1 b x x 1 1 dx lim 2 dx lim ( ln( x 2 1) 1b [lim ln( b 2 1)] , divergent. b 1 x 1 b 2 2 b x 1 2 : divergent b) The function is undefined at x=1. Approach 1 from the right hand side. lim b 1 15) 1 dx lim [ln 2 ln( b 1)] : b x 1 b 1 3 divergent. Thus y is always x2 x3 x3 x4 ..) x x 2 ... 2! 3! 2 6 0.1 0.1 x3 x4 x2 x3 x4 x5 0.12 0.13 0.14 x 2 0.1 xe dx ( x x ...) dx ( ...) ( ) . 0 0 0 2 6 2 3 8 30 2 2 8 0.1 0 . 14 0.12 0.13 4 xe x dx By trial and error, is the first term with value less than 10 . Thus 0 8 2 3 k ( k 1 ) k ( k 1 )( k 2 ) k Use the binomial formula: (1 x) 1 kx x2 x3 . 2 6 1 1 1 1 3 1 1 1 ( ) 2 ( )( ) 2 2 1 2 x x x 2 ( x )3 (2 x 2 ) 3 2 3 (1 ) 3 2 3 [1 2 2 ( )2 2 2 2 2 2 2 6 2 1 1 1 2 2 0.14 x 1 4 1 6 0.1 1 1 2 3 [1 x x 00.1 2 3 [1 0.14 0.16 By trial and error, 2 3 is 32 2 32 128 2 32 128 a) )First observe that the Maclaurin series for b) the first term with value less than 10 4 xe x is x(1 x . Thus the integral 0.1 3 0 1 3 2 x dx 2 [1 2 0.12 ] 2 16) First check for the absolute convergence: use the comparison test to show 2n n 1 n 2n 1 2 n 11 . 2 3n 2n n 2 n 2 1 is divergent. The smaller series is divergent by the p-test. Thus the series does not converge absolutely. Next check for conditional using the alternate series test. a) b) d n 2n 2 1 ( ) The terms are decreasing since its derivative is negative. dn 2n 2 1 (2n 2 1) 2 n 0 . Thus the series converges conditionally. Using L’hopital, lim 2 n 2n 1 17 ) Use Newton’s law of cooling: We can set 12 pm to be t=0. Then at 1 pm t=1. We have T (0) 80, T (1) 75 . We need to find t when T=98. The room temperature TM 70 dT dT k (T 70) kdt ln T 70 kt c T 70 e c e tt . Now remove the absolute value dt (T 70) c kt by taking on the right hand side. We let e A . We have T 70 Ae . When t=0, T=80. 1 1 80 70 Ae0 A 10 . When t=1, T=75: 75 70 10e k e k k ln( ) ln 2 k ln 2 2 2 t ln 2 The equation now becomes T 70 10e . Find t when T=98. ln 2 . 8 98 70 10e t ln 2 2.8 e t ln 2 t 1.5 . Thus the murder took place at 10:30 a.m. ln 2 18) a) This is a geometric series with common ratio 1 e and a1 1 . Thus e n 0 n a1 1 r 1 1 1 e e e 1 (1) n ( ) 2 n1 sin 1 (2n 1)! n 0 2 1 1 c) This is telescoping. First apply the partial fraction technique to get . Then (2n 1)( 2n 1) 2n 1 2n 1 1 1 1 1 1 1 1 1 1 th nth partial sum is s n ( ) )( ) ( ) ( Thus ) 1 1 3 3 5 5 7 2n 1 2n 1 2n 1 2 1 lim (1 ) 1 n 2n 1 n 1 ( 2n 1)( 2n 1) b) This is the power series of sinx with 19)a) Use the formula L b a x . Thus dx dy ( ) 2 ( ) 2 dt . dt dt 4 0 1 4 3 9 1 ( t 2 ) 2 dt 1 t dt : 0 2 4 1 let 3 4 10 4 2 9 9 u 1 t du dt , t 0 u 1, t 4 u 10 . Thus u 2 du ( (10 2 1)) 1 4 4 9 9 3 2 3 3 3 x ln x 1 1 1 b) f ( x) , 1 x 3 L 1 f ' ( x) 2 dx 1 ( x ) 2 dx 1 ( x 2 )dx 1 1 1 2 4 4x 2 16 x 2 1 3 3 3 1 1 2 1 2 1 2 ( x ) dx ( x ) dx ( x )dx 2 1 1 1 2 16 x 4x 4x 2 x 1 9 1 1 1 ( ln x) 13 ( ln 3) 4 ln 3 2 4 2 4 2 4 20) ) A) i) For dx, the integral needs to be broken up into two pieces as the top equation changes 0 1 ii) 1 ( x 1)dx ( x 1) 2 dx 0 For dy, first solve the equation for x: do not use Area= y y x 1 x y 1 since the y-values are positive. and y ( x 1) 2 x 1 y . x y 1 1 0 [( y 1) ( y 1)]dy B) X First find the points of intersection: a) For dx, x 2 2 x 2 x 1 1 1 [( 2 x 2 ) x 2 ]dx b) For dy, first solve for x: y x2 x y . y x2 2 x 2 y But Area= 1 0 2 ( y ( y )) dy ( 2 y ( 2 y )) dy 1 21) a) f ( x) e 4 x f ( 4) ( x) 256e 4 x . Thus error The maximum of 256e 4 x for 0 x4 is 246e16 256e16 (4)5 180(6) 4 c) f ( x) 1 2 f ( 2 ) ( x) 1 x (1 x) 3 The maximum of 2 (1 x) 3 2(4) 3 2(4) 3 error 0.001 n 103.3 104 12(n) 2 12(0.001) for 0 x4 is 2 2 (1 0) 3
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