x+1分之1+2=
=[1+2(x+1)]/(x+1)
=(2x+3)/(x+1)
2x分之y+（3x的平方）分之y=
=(3xy+y)/6x²
（a的平方-4）分之（a-6）+(a-2)分之1
=[(a-6)+(a+2)]/(a+2)(a-2)
=(2a-4)/(a+2)(a-2)
=2/(a+2)