if cos(1/2)x=(√5)/4 what is the value of cos^2x?1)1/64 2)1/4 3)9/_英语解答

if cos(1/2)x=(√5)/4 what is the value of cos^2x?1)1/64 2)1/4 3)9/64 4)16/25

人气：305 ℃　时间：2020-05-26 06:31:07

解答

3)9/64
Half-Angle formula:cos(x)=2cos(x/2)^2-1
In this question:cos(x/2)^2 = 5/16
So:cos(x) = 2(5/16)-1=-3/8
So:(cos(x))^2=(-3/8)^2=9/64