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(3)原式=∫(1,2)dy∫(y,y^2)sin(πx/2y)dx
=∫(1,2)dy*[-(2y/π)*cos(πx/2y)|(y,y^2)]
=∫(1,2) (-2y/π)*cos(πy/2)dy
=∫(1,2) (-4y/π^2)*d[sin(πy/2)]
=(-4y/π^2)*sin(πy/2)|(1,2)+∫(1,2) (4/π^2)*sin(πy/2)dy
=4/π^2-(8/π^3)*cos(πy/2)|(1,2)
=4/π^2+8/π^3
=∫(1,2)dy*[-(2y/π)*cos(πx/2y)|(y,y^2)]
=∫(1,2) (-2y/π)*cos(πy/2)dy
=∫(1,2) (-4y/π^2)*d[sin(πy/2)]
=(-4y/π^2)*sin(πy/2)|(1,2)+∫(1,2) (4/π^2)*sin(πy/2)dy
=4/π^2-(8/π^3)*cos(πy/2)|(1,2)
=4/π^2+8/π^3
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