Question

cos52*+cos68*+cos172*=?????
please help me I'M IN TROUBLE

Answer 1

Given cos 52 + cos 68 + cos 172

= > (cos 52 + cos 68) + cos(172)

= > we know that cos a + cos b = 2 cos(a + b)/2 cos (a - b)/2

= > 2 [cos(68 + 52)/2] [cos (68 - 52)/2] + cos(180 - 8)

We know that cos(180 - A) = -cosA

= > 2 cos (60) cos (8) - cos 8

= > 2 (1/2) cos 8 - cos8

= > cos8 - cos8

= > 0.

Hope this helps!