Honors Geometry_11.3_April 6
Warmup
1) The sides of a parallelogram have lengths 14 in. and 20 in. and
one of the angles of the parallelogram has a measure of 45˚.
Find the area.
3) An equilateral triangle has perimeter of 36 ft. Find the area. Draw a
picture.
2) Find the area of the purple region.
12 ft
7 ft
5 ft
20 ft
11.3
Areas of
Trapezoids
perpendicular to a line
An altitude of a trapezoid is any segment ________________
containing a base from a point on the opposite base.
Since the bases are parallel, all altitudes have
height (h)
the same length, called the
Theorem 11-5:
half
The area of a trapezoid equals ________
the product of the height and
the sum of the bases.
Learning target:
I can ... find the area of a trapezoid.
Atrapezoid = ½ h (b1 + b2)
1
Honors Geometry_11.3_April 6
Ex 1
Find the area of a trapezoid with height 7 and bases 12 and 8.
Ex 2
Find the area of an isosceles trapezoid with legs 5 and
bases 6 and 10.
=
=
=
Recall:
Ex 3 Find the area.
How did we find the length of the median?
Ex 4 Find the area.
45º
3√2
4
That means we can also find the area of trapezoid using:
Atrapezoid = (height)(median)
2
Honors Geometry_11.3_April 6
Ex 5
Find the median and the area of the trapezoid.
Ex 7 Find the area and the second base of a trapezoid
with height = 3, base1 = 3 and median = 5.
=
A = 15
=
Ex 6
A trapezoid has an area of 75 cm2 and a height of 5 cm.
How long is the median?
Ex 8 The perimeter of a trapezoid is 35. The nonparallel
sides are 7 and 8. Find the area if the height is 5.
11.3 Assignment:
P. 436 #'s WE 1-13 odd; 16-22 even, 30
Perimeter
35 =
+
3
Honors Geometry_11.3_April 6
Answers to 11.3 homework
Need find the height for #30
1) A= 70, m=10
3) A=6, m = 3 3/4
5) h=5, m=18
7) b=1, m=4
9) 9
11) 108
13) 27 3
4
16) 180
18) 65
20) 71.0
22) 120, 17, 17
30) 204
x=5
so 169 - 25 = 144
height = 12
4