Question

Given:cosA= 4/5 0(less than or equal to)A(less than of equal to)90*

find sinA, sin2A, cos2A

Answer 1

cosA = 4/5 or opposite = 4, hypotenuse = 5
you should recognize the 3-4-5 triangle,

then sinA = 3/5

sin 2A = 2sinAcosA = 2(3/5)(4/5) = 24/25

cos 2A = cos^2 A - sin^2 A
= 16/25 - 9/25 = 7/25

Answer 2

thank you.