Question

Find cos (2 theta angle) if sin (theta angle) =4/5

Answer 1

sin(theta) = 4/5,
`cos^(2) (theta)=1-( (4)/(5))^(2) = 1 - (16)/(25) = (9)/(25)` We will switch it to formula:
`cos(2 theta)=cos^(2) (theta)-sin^(2) (theta)= (9)/(25) - (16)/(25)=- (7)/(25)`