(1):(x+2y)+4y²/(x-2y)
=[(x+2y)(x-2y)+4y²]/(x-2y)
=x²/(x-2y)
(2):(x²+4x+3)/(x²+2x+1)
=[(x+1)(x+3)]/(x+1)²
=(x+3)/(x+1),所以
原式=x/(x²-1)/[(x+3)/(x+1)](我想你应该是打错了吧)
=[x/(x+1)(x-1)]×[(x+1)/(x+3)]
=x/[(x-1)(x+3)]=x/(x²+2x-3)
(3):原式=12/[(m-3)(m+3)]+2/(3-m)
=12/[(m-3)(m+3)]-2/(m-3)
=[12-2(m+3)]/[(m-3)(m+3)]
= -2(m-3)/[(m+3)(m-3)]
=-2/(m+3)