Anonymous

cos(a-b) = cos(a)cos(b)+sin(a)sin(b) cos(180-θ) = cos(180)cos(θ)+ sin(180)sin(θ) We know that cos(180)=-1 sin(180)=0 Plug n chug cos(180-θ) = -cos(θ)+ (0)sin(θ) cos(180-θ) = -cos(θ) It is not possible to rewrite the given expression using sine or tangent.

Anonymous

cos(a-b) = cos(a)cos(b)+sin(a)sin(b) cos(180-θ) = cos(180)cos(θ)+ sin(180)sin(θ) cos(180)=-1 sin(180)=0 cos(180-θ) = (-1)cos(θ)+(0)sin(θ) = -cos(θ) =-sqrt(1-sin^2(θ))