https://puu.sh/y4Ose/987fce7804.png
Could anyone explain how I go about solving this? Thank you!
cosθ = .7
cosθ + cos ( θ + 2pi) + cos ( θ + 4pi)
Use cos (A + B) = [ cosAcosB - sinAsinB ]
cos θ + [ cosθ cos (2pi) - sinθ sin (2pi) ] + [ cosθ cos (4pi) - sinθ sin (4pi) ]
cos θ + [ cos θ - 0 ] + [ cos θ - 0 ]
3 cosθ
3 ( .7) = 2.1
