a) sin^2x + cos^2x = 1 $identity$

b) sin^2x / $1+co{s}^{2}x$ = sin^2x $asthedenominatorcancelsout$

c) cos^2x - cosx / $1-sinx$ = 0

d) No option provided

e) cos3x - cosx / sinx = 2cos^2x - 1 $viatrigonometricidentities$