Question

prove that 2sin70°*cos20°=cos50°

Answer 1

Answer:

L.H.S.:

$= > 2 \sin(70) \times \cos(20)$

$= > 2 \cos(\pi - 70) \times \cos(20)$

$= > \cos(70 + 20) + \cos(70 - 20)$

$= > \cos(90) + \cos(50)$

$= > 0 + \cos(50)$

$= > \cos(50°) = r.h.s.$

Hence, proved.

Hope this answer helps you ^_^ !

Answer 2

$\huge \tt{we \: know \: that}$

➡2 cos A. cos B = cos (A+B)+cos (A- B)

= cos ( 70+20+ cos (70-20)

= cos 90° + cos 50 °

➡we know that cos 90= 0

= cos 50

⭐hence proved