1+(color(red)(sin^2theta))/(cos^2theta)1+sin2θcos2θ
Use the following identity to solve for sin^2thetasin2θ
sin^2theta+cos^2theta=1sin2θ+cos2θ=1
sin^2theta=color(red)(1-cos^2theta)sin2θ=1−cos2θ
Substitute this instead of sin^2thetasin2θ
1+(sin^2theta)/(cos^2theta)=1+(color(red)(1-cos^2theta))/cos^2theta1+sin2θcos2θ=1+1−cos2θcos2θ
Add 11 and (1-cos^2theta)/cos^2theta1−cos2θcos2θ together by unifying the denominators (11 is
the same as cos^2theta/cos^2thetacos2θcos2θ), so
color(red)1+(1-cos^2theta)/cos^2theta=color(red)(cos^2theta/cos^2theta)+(1-cos^2theta)/cos^2theta1+1−cos2θcos2θ=cos2θcos2θ+1−cos2θcos2θ
=(cancel(cos^2theta)+1cancel(-cos^2theta))/cos^2theta
=1/cos^2theta
=sec^2theta