If the angles made by a straight line with the coordinate axes are $\alpha, \frac{\pi}{2}-\alpha, \beta$,then $\beta$ is equal to

$\int \frac{dx}{a^2 \sin^2 x + b^2 \cos^2 x}$ is equal to

Which of the following substances does not contain a $-COOH$ group?

$A$ plano-convex lens fits exactly into a plano-concave lens. Their plane surfaces are parallel to each other. If the lenses are made of different materials of refractive indices $\mu_1$ and $\mu_2$ and $R$ is the radius of curvature of the curved surface of the lenses,then the focal length of the combination is

Let $P$ be a plane passing through the points $(2,1,0)$,$(4,1,1)$ and $(5,0,1)$ and $R$ be the point $(2,1,6)$. Then the image of $R$ in the plane $P$ is

In the following structure,the double bonds are marked as $I, II, III$ and $IV$. Geometrical isomerism is not possible at site$(s)$: