X区域：D：x = 2,y = 1,y = x ==> 1 ≤ x ≤ 2,1 ≤ y ≤ x∫∫_D xy dxdy= ∫(1→2) dx ∫(1→x) xy dy= ∫(1→2) [xy²/2]：(1→x) dx= ∫(1→2) (x³/2 - x/2) dx= [x⁴/8 - x²/4]：(1→2)= (2...