h > 0 ==> z = (h/R)√(x² + y²)
截面：x² + y² = R²,- √(R² - x²) ≤ y ≤ √(R² - x²)
∫∫∫ z dxdydz
= ∫(- R→R) dx ∫(- √(R² - x²)→√(R² - x²)) dy ∫(0→h) z dz
= (1/2)h²∫(- R→R) dx ∫(- √(R² - x²)→√(R² - x²)) dy
= (1/2)h²∫(- R→R) 2√(R² - x²) dx
= 2h²∫(0→R) √(R² - x²) dx,x = Rsinp,dx = Rcosp dp
= 2h²∫(0→π/2) R²cos²p dp
= h²R²∫(0→π/2) (1 + cos2p) dp
= h²R² * [ p + (1/2)sin2p ] +(0→π/2)
= h²R² * π/2
= (1/2)πh²R²