高数,二重积分,我需要详细步骤,谢谢(๑•ั็ω•็ั๑)
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对于本题,∫∫<D>f(x, y)dxdy必为常数,记为 A,则
f(x, y) = xy + A
积分域 D 的面积 σ = ∫<0, 1> x^2dx = 1/3
f(x, y) = xy + A 两边在 D 上积分,得
A = ∫∫<D>xydxdy + Aσ
= ∫<0, 1>xdx∫<0, x^2>ydy + A/3
= (1/2)∫<0, 1>x^5dx + A/3
= 1/12 + A/3
2A/3 = 1/12, A = ∫∫<D>f(x, y)dxdy = 1/8
f(x, y) = xy + A
积分域 D 的面积 σ = ∫<0, 1> x^2dx = 1/3
f(x, y) = xy + A 两边在 D 上积分,得
A = ∫∫<D>xydxdy + Aσ
= ∫<0, 1>xdx∫<0, x^2>ydy + A/3
= (1/2)∫<0, 1>x^5dx + A/3
= 1/12 + A/3
2A/3 = 1/12, A = ∫∫<D>f(x, y)dxdy = 1/8
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