Remember: The trigonometric identities '
sin^2theta+cos^2theta= 1 hArr sin^2theta= 1-cos^2theta
1/costheta= sectheta hArr 1/sectheta= costheta
(1+sectheta)/sectheta = (sin^2theta)/(1-costheta)
=> If we start from the right hand side, multiply by the conjugate of the denominator
(1+sectheta)/sectheta = [(sin^2theta)/(1-costheta)]color(red)([(1+costheta)/(1+costheta)]
(1+sectheta)/sectheta = ((sin^2theta)(1+costheta)]/(1-cos^2theta)
(1+sectheta)/sectheta = [(sin^2theta)(1+costheta)]/(sin^2theta)
(1+sectheta)/sectheta = [cancel(sin^2theta)
(1+costheta)]/(cancel(sin^2theta)
(1+sectheta)/sectheta = 1+costheta
(1+sectheta)/sectheta = 1+1/(sectheta) common denominator
(1+sectheta)/sectheta = 1*[color(red)sectheta]/color(red)sectheta+1/(sectheta)
(1+sectheta)/sectheta = (1+sectheta)/sectheta
Done!