Vectors a and b have scalar product -3.00 and their vector product has magnitude 5.00. what is the angle between these two vectors?

A.b = [a][b]cosθ

a.b = scalar product = -3

 [a][b] = vector product = 5

a.b = [a][b]cosθ

-3 = 5cosθ

(-3/5) = cosθ

-0.6 = cosθ

cosθ = -0.6

Take the arc cos of both sides.

θ = cos⁻¹(-0.6)

θ ≈ 126.87°             using a calculator.

The angle between the two vectors ≈ 126.87°

Hope this helps.