x的平方+x分之1+x的平方+3x+2分之1+x的平方-2x分之 2
=1/(x²+x)+1/(x²+3x+2)+2/(x²-2x)
=1/x(x+1)+1/(x+1)(x+2)+2/x(x-2)
=1/x-1/(x+1)+1/(x+1)-1/(x+2)+2/x(x-2)
=1/x-1/(x+2)+2/x(x-2)
=(x²-4-x²+2x+2x+4)/x(x²-4)
=4x/x(x²-4)
=4/(x²-4)