令x = sinθ，dx = cosθdθ∫(0~1) √(1 - x²) dx= ∫(0~π/2) cos²θ dθ= (1/2)∫(0~π/2) (1 + cos2θ) dθ= (1/2)(θ + 1/2 • sin2θ) |(0~π/2)= (1/2)(π/2)= π/4
