Aim #43: What is the Law of Cosines?
HW Packet Due Wednesday 12/21
Quiz (Aims 40-44) Thursday 12/22
Do Now:
o
In ABC, b = 8, c = 7 and angle B = 45 . Find the measure
of angle C to the nearest unit using the Law of Sines.
In
ABC, b = 8, c = 7 and angle A = π/4. Find a to the nearest unit.
Law of Cosines
• must be the same
• one must be the unknown
We use
law of cosines
if we know:
-two sides and the included angle (to find the third
side)
-all three sides (to find an angle measure)
Solve for x, to the nearest tenth. B
x
20
35o
A
14
C
E
x
Solve for x to the nearest unit. 8
62o
D
5
In ΔABC, b = 4, c = 7, and cos A = 3/5. What is the value of a, to the nearest tenth?
In Δ DEF, d = 4, e = 7, and f = 8. What is the measure of <F?
What is the measure of the largest angle in Δ ABC?
C
8
A
5
12
B