two straight roads PC, PD at right angles to one another, running up a hill ABCD which is inclined at an angle theta to the horizontal. The roads PC, PD are inclined at angles a,b to the horizontal. BC, AD are lines of greatest slope and AB is the horizontal; CE, DF are verticals from C,D to the horizontal plane.

Show that sinsquaredtheta = sinsquareda + sinsquaredb

AHH pLEASE HELP, im SO LOST ! T.T

any help is GREATLLYYY APPRECIATED !!

THANKYOU in advancee