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.
