∫[0,π]cos^4xdx
=∫[0,π]((cos2x+1)/2)²dx
=(1/4)∫[0,π](cos²2x+1+2cos2x)dx;
=(1/4)∫[0,π]((cos4x+1)/2+1+2cos2x)dx
=(1/4)((1/8)sin4x+3x/2+sin2x)|[0,π]
=(1/4)(3π/2)
=3π/8
∫[0,π]cos^4xdx
=∫[0,π]((cos2x+1)/2)²dx
=(1/4)∫[0,π](cos²2x+1+2cos2x)dx;
=(1/4)∫[0,π]((cos4x+1)/2+1+2cos2x)dx
=(1/4)((1/8)sin4x+3x/2+sin2x)|[0,π]
=(1/4)(3π/2)
=3π/8