Explanation:

To find the angle between two equal forces, we need to use the formula for the resultant force:

R = √(F1² + F2² + 2F1F2cosθ)

where F1 and F2 are the magnitudes of the two equal forces, θ is the angle between them, and R is the magnitude of the resultant force.

We are given that the resultant force is double the magnitude of either force, so we can write:

R = 2F1 = 2F2

Substituting this into the formula for the resultant force, we get:

2F1 = √(F1² + F2² + 2F1F2cosθ)

Squaring both sides, we get:

4F1² = F1² + F2² + 2F1F2cosθ

Simplifying, we get:

3F1² - F2² = 2F1F2cosθ

Dividing both sides by 2F1F2, we get:

cosθ = (3F1² - F2²) / (2F1F2)

Answer:

The angle between the two equal forces is given by:

θ = cos⁻¹[(3F1² - F2²) / (2F1F2)]

This formula gives the angle between the two forces in terms of their magnitudes. To find the numerical value of the angle, we need to know the values of F1 and F2, which are not given in the problem.