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Question
If x = r cos A cos B, y = r cos A sin B and z = r sin A, show that : x2 + y2 + z2 = r2
Solution
L.H.S. = x2 + y2 + z2
= (r cos A cos B)2 + (r cos A sin B)2 + (r sin A)2
= r2 cos2 A cos2 B + r2 cos2 A sin2 B + r2 sin2 A
= r2 cos2 A (cos2 B + sin2 B) + r2 sin2 A
= r2 (cos2 A + sin2 A)
= r2 = R.H.S.
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