To prove that the trignometric identity sinθ cot θ is equal to cos θ, you can use the following:
sinθ cotθ = cosθ sinθ(cosθ/sinθ) = cosθ
cancel sinθ on the numerator and denominator and you will get:
cosθ = cosθ
I believe the answer is -2, 7
13, 37, 109, 325, 973. Hope that helps!