Answer:
120°
Explanation:
From the question,
The expression for the dot product of two vector is given as
a.b = abcosθ................... Equation 1
make θ the subject of the equation
θ =cos⁻¹ (a.b/ab)......................... Equation 2
Where θ = angle between the vector.
Given: a.b = -27, a = 6, b = 9
Substitute these values into equation 2
θ = cos⁻¹[-27/(6×9)]
θ = cos⁻¹(-27/54)
θ = cos⁻¹(-0.5)
θ = 120°.
Hence the angle between the vector is 120°