Given, and

We know the cross product of two vectors and forming an angle θ is

where is a unit vector perpendicular to and

is a unit vector

⇒ 8 = 2 × 5 × sin θ × 1

⇒ 10 sin θ = 8

We also have the dot product of two vectors and forming an angle θ is

But, we have sin²θ + cos²θ = 1

Thus,