x = rcosθ,y = rsinθx² + y² = 2x(rcosθ)² + (rsinθ)² = 2rcosθr²(cos²θ + sin²θ) = 2rcosθr = 2cosθ∫∫_D √(4 - x² - y²) dxdy= ∫(0,π/2) ∫(0,2cosθ)...