If x = r cos a cosb cos c, y = cosa cosb sinc, z = r sina cosb u = r sinb then x square + y square + z square + u square =

Hi,

Follow the following steps :

Substitute the values in the expression. Observe the first term and second term carefully. If you take whatever common than this will be COMBINED one term.
Than this term will be combined with the third term and similarly with fouths term. The final answer will be r^2.