# In $\sin x=-\cos^2x$ then $\cos^2x(1+\cos^2x)$ equals

$(a)\;0\qquad(b)\;1\qquad(c)\;2\qquad(d)\;None\;of\;these$

$\cos^2x(1+\cos^2x)=\cos^2x+\cos^4x$
$\qquad\qquad\qquad\quad=\cos^2x+\sin^2x$
$\cos^2x+\sin^2x=1$
$\qquad\qquad\qquad\quad=1$
Hence (b) is the correct answer.