Question

Which of these is equal to sin(70°)? A) cos(110°) B) cos(160°) C) cos(20°) D) cos(70°)

Answer 1

sin β = cos (90-β)
sin (70⁰)= cos (90-70⁰)=cos (20⁰)
sin (70⁰)=cos (20⁰)

Answer 2

`sin (70^(\circ))=cos (20^(\circ))`

Option C is correct.

Explanation:

we have to choose the option for which the value is equals to sin(70°)

As in the first quadrant sine and cosine both are positive

`\sin \theta = \cos (90-\theta)\\\\\sin (70^(\circ))= \cos (90-70)=\cos (20^(\circ))\\\\sin (70^(\circ))=cos (20^(\circ))`

hence, option C is correct.