Why sin (pi/2 + x ) =cosx

This question was asked in Example 14

Piyush Mishra

July 26, 2017, 9:01 p.m.

Answers!

Davneet Singh

July 27, 2017, 1:15 p.m.

Hello Piyush,

sin (pi/2 + x) = cos x is a formula

Here is how we derive it

$sin (a + b) = sin a cos b + cos a sin b$

$sin (\frac{π/}{2} + x) = sin (\frac{π/}{2}) \cdot cos x + cos (\frac{π/}{2}) . sin (x)$

$Since, sin (\frac{π/}{2}) = 1 &$ $cos (\frac{π/}{2}) = 0$

So we have :

$sin (\frac{π/}{2} + x) = cos x$

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