(a) Show that cos A + cos(120° + A) + cos(120° - A) = 0.

Question

asked Jul 21, 2024 153k views

1 Answer

DwB · Answer 1 · 2024-07-28T20:36:43+0000

Explanation:

Using the two trig identities (shown below)

= cos A + cos 120 cos A - sin 120 sinA + cos 120 cos A + sin120 sinA

= cos A + 2 cos 120 cos A cos 120 = -1/2

= cos A + 2 ( -1/2) cosA

= cos A - cos A

= 0