if cos theta =7/13, where 0<theta<pi/2, fin the value of cos2theta

Answer 1

If you mean to find the value of cos(2θ) given cos(θ)=7/13, then use the double angle formula:

cos(2θ)=cos²(θ)-sin²(θ)

where:
sin²(θ)
=(1-cos²(θ))
=120/169