Determine the value of cos 2θ given, cos θ = 3 5 and 0 ≤ θ ≤ π 2 .

Answer 1

cosx = 3/5

cos2x = cos^2(x) -sin^2(x) = 9/25 - 16/25 = -7/25

cos2x=-.28

x=53.13 or -53.13 =306.87

2x=106.26 or 613.74

cos106.26=-,28=-7/25

cos613.74=-.28