Question

$\sin(90 +thita )$

Answer 1

Sin(90 + theta) = Cos (theta)
hope it helps...

Answer 2

Hey 

→ sin ( A + B ) = sin A cos B + sin B cos A 

Note : sin( - A ) = - sin A  [ this can be very helful ]

→ sin ( 90° + θ ) = sin90° cosθ + cos 90° sinθ

=> sin ( 90° + θ ) = cos θ + 0 = cos θ
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Another way to arrive at this :

→ cos ( -θ ) = cos θ
 
Use : sin( 90° - x ) = cos x

=> sin ( 90° - ( -θ ) ) = cosθ

=> sin ( 90° + θ ) = cos θ