We have, L.H.S. =

cos(π+x)cos(−x)

sin(π−x)cos( π 2 +x)

=

−cosxcosx

sinx(−sinx)

= cot2 x = R.H.S.
[Since cos (π+ θ) = - cos θ , cos (

π

2

+θ) = - sin θ
cos (- θ) = cos θ , sin (π - θ) = sinθ]