Explanation

For the X and Y components of a force to be equal:

Fx = Fy

Given F = Fx i + Fy j = F cos(θ) i + F sin(θ) j

Fx = F cos(θ)

Fy = F sin(θ)

For Fx = Fy:

F cos(θ) = F sin(θ)

cos(θ) = sin(θ)

tan(θ) = 1

θ = 45°