1.a-b+(2b²)/(a+b)
=[(a-b)(a+b)+2b^2]/(a+b)
=(a^2+b^2)/(a+b)
2.(x-2)/x²÷(1-x/2)
=(x-2)/x^2÷(2-x)/2
=(x-2)/x^2*2/(2-x)
=-2/x^2
3.(4+x)/(x-1)-5=(3+2x)/(x-1)
(4+x-3-2x)/(x-1)=5
(1-x)/(x-1)=5 /感觉有问题