x = kt,dx = k dt
y = a cost,dy = - a sint dt
z = a sint,dz = a cost dt
t：0→π
∮Γ (x² + y² + z² - a²)dx + zdy - ydz
= ∫(0→π) [(k²t² + a² cos²t + a² sin²t - a²)(k) + (a sint)(- a sint) - (a cost)(a cost)] dt
= ∫(0→π) (k³t² - a²) dt
= (1/3 * k³t³ - a² t)：(0→π)
= (1/3)k³π³ - a²π