26. If $y = f ( x )$ and $y \cos x + x \cos y = \Pi$, then the value of $f ^ { \prime } ( 0 )$ is : (a) $\sqcap$ (b) $- \Pi$ (c) 0 (d) $2 \Pi$
Suppose $\mathbf { a , b , c }$ are three non-zero, non-coplanar vectors. Let
26. If $y = f ( x )$ and $y \cos x + x \cos y = \Pi$, then the value of $f ^ { \prime } ( 0 )$ is :\\
(a) $\sqcap$\\
(b) $- \Pi$\\
(c) 0\\
(d) $2 \Pi$\\