4.5 Prove Trigonometric Identities

The basic trigonometric identities are the Pythagorean identity, the quotient identity, the reciprocal identities, and the compound angle formulas.

To prove that an equation is an identity, treat each side of the equation independently and transform the expression on one side into exact form of the expression on the other side.

Example :

Prove that cos(π/2 - x ) = sinx

How?

L.H.S            

cos (π/2 - x ) 

= cos  π/2 cos x + sin π/2 sin x

= 0 x cos x + 1 x sin x 

R.H.S

sin x

Thus, L.H.S. = R.H.S 

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