计算:a/(a+1)^2+1/(a+1)^2 =(a+1)/(a+1)^2=1/(a+1)
,2x/x^2-64y^2-1/x-8y
=2x/(x^2-64y^2)-(x+8y)/(x-8y)(x+8y)
=(2x-x-8y)/(x-8y)(x+8y)
=1/(x+8y)