四.令x=1,则d 2 , 01+X +o01+t dt=0 1+x 令I=1+x4 2I= 1x+)1+x 1+x dx 1+x 01+x K心四. , 1 , 1 2 dt t dx t 令 x = 则 = − , 1 1 1 1 1 1 1 0 4 2 0 4 2 0 4 2 0 4 dx x x dt t t t dt t dx x     + + + + + = + − = + − = + , 1 1 0 4 dx x I  + + 令 = dx x x dx x I   + + + + + = 0 4 2 0 4 1 1 1 2 dx x x  + + + = 0 4 2 1 1