#sin theta +cos theta=(2sin^2theta-1)/(sin theta-costheta)#
Left Side:#=sin theta +cos theta#
#=(sin theta +cos theta)/1*(sintheta-costheta)/(sintheta-costheta)#
#=(sin^2theta-cos^2theta)/(sin theta -cos theta)#
#=(sin^2theta-(1-sin^2theta))/(sin theta -cos theta)#
#=(sin^2theta-1+sin^2theta)/(sin theta -cos theta)#
#=(sin^2theta+sin^2theta-1)/(sin theta -cos theta)#
#=(2sin^2theta-1)/(sin theta -cos theta)#
#:.=#Right Side