=(x+2+x-2)/(x平方-4)+2x/(x平方+4)+4x三次方/（x四次方+16）=2x/(x平方-4)+2x/(x平方+4)+4x三次方/（x四次方+16）=(2x三次方+8x+2x三次方-8x)/(x四次方-16)+4x三次方/（x四次方+16）=4x三次方/(x四次方-16)+4x三次...