Find the coefficients of the fourier sine series
f(x) = ₖ=₁∑[infinity] Bₖ sin (πkx/L)

for the function defined by
f(x) = {0 x ∈ (0, 1/4)
{1 x ∈ (1/4, 3/4)
{0 x ∈ (3/4, 1)

use pi for π. Give the general form of the coefficient Bₖ