If sin3A=3/5, what is cos3A?
Show answer & explanation
Correct answer: A
Explanation
sin3A = 3/5
According to the formula:
sin²θ + cos²θ = 1
sin²3A + cos²3A = 1
(3/5)² + cos²3A = 1
9/25 + cos²3A = 1
cos²3A = 1 − 9/25= 16/25
cos3A = √(16/25) = 4/5