(4/m^2-4)-(1/m-2)
=4/(m+2)(m-2) -1/(m-2)
=4/(m+2)(m-2)-(m+2)/(m+2)(m-2)
=(4-m-2)/(m+2)(m-2)
=(2-m)/(m+2)(m-2)
=-1/(m+2)
2.x+y-(x^2+y^2/x+y)
=(x+y)²/(x+y)-(x²+y²)/(x+y)
=[(x+y)²-x²-y²]/(x+y)
=2xy/(x+y)
3.1-(x乘以1/1-x)
=1+x/(x-1)
=(x-1+x)/(x-1)
=(2x-1)/(x-1)