原式=-(a^2-2a+1)/(a^2+a-2) = -(a-1)^2/(a+2)(a-1) = -(a-1)/(a+2)
原式=(2a^3b^4-6a^2b^3)/(a^2b^2+2ab-15)= 2a^2b^3(ab- 3)/(ab+1)^2-16 = 2a^2b(ab- 3)/(ab+1+4)(ab+1-4) = 2a^2b(ab^3- 3)/(ab+5)