Question

if sin a=0.4 what is the value of cos 2a

(A) 0.64
(B) 0.86
(C) 0.68
(D) 0.14​

Answer 1

Answer:

cos

$cos2a = 1 - 2 {sin}^{2} a \\ = 1 - 2 ({0.4}^{2} ) \\ = 1 - 2 \times 0.16 \\ = 1 - 0.32 \\ = 0.68$