How do you prove $sin (x- (pi/2))= cos x$ ?

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Answer 1 · 2016-04-09T03:16:24

The right hand side should be $- cos x$
Expand $sin(x-pi/2)$ using $sin(a-b)=sin a cos b-cos a sin b$ .

Prove $sin (x-pi/2 )=-cos x$ .

Using $sin(a-b)=sin a cos b-cos a sin b$ ,
$sin (x-pi/2)=sin x cos (pi/2)-cos x sin (pi/2) = 0- cos x$ .

How do you prove sin (x- (pi/2))= cos x sin (x- (pi/2))= cos x ?