The angle between two vectors of magnitude 12 and 18 units

The angle between two vectors of magnitude 12 and 18 units when their resultant is 24 units, is

We know that, R^{^→} = A² + B² + 2AB cosθ
(24)² = (12)² + (18)² + 2(12) (18) cosθ

cosθ =	108	⇒ θ = 75°52'
	432