思考题解答 ()不能直接积出,改变积分次序 令Ⅰ=|dxf(x)f(y)y, 则原式=小y(x)()=(x))o, 故2Ⅰ=f(x)dxf(y)dy ∫(x)d(+)(y)d /(x)(y)=思考题解答  1 ( ) x  f y dy不能直接积出,  改变积分次序. 令   = 1 1 0 ( ) ( ) x I dx f x f y dy, 则原式   = y dy f x f y dx 0 1 0 ( ) ( ) ( ) ( ) , 0 1 0  = x f x dx f y dy 故   = 1 1 0 2 ( ) ( ) x I f x dx f y dy ( ) [( ) ( ) ] 1 0 1 0 f x dx f y dy x x    = + ( ) ( ) . 2 1 0 1 0 = f x dx f y dy = A  