The angle of elevation of an object from a point P on the level ground is $\alpha$. Moving d meters on the ground towards the object. the angle of elevation is found to be $\beta$. Then the height (in meters) of the object is

Question

$$\begin {array} {1 1} (a)\;d \tan \alpha & \quad (b)\;d \cot \beta \\ (c)\;\frac{d}{\cot \alpha+\cos \beta} & \quad (d)\;\frac{d}{\cot \alpha - \cot \beta} \end {array}$$