Question
Find cos2A when cosA = -3/5 and π/2<A<π.
A) -24/25
B) -7/25
C) 7/24
D) 24/7
A) -24/25
B) -7/25
C) 7/24
D) 24/7
Answers
Steve
just use the double-angle formula:
cos2A = 2cos^2 A - 1
cos2A = 2cos^2 A - 1