（x+1）（x+2）分之1+（x+2）（x+3）分之1=3分之21/(x+1)-1/(x+2)+1/(x+2)-1/(x+3)=2/31/(x+1)-1/(x+3)=2/3乘以3(x+1)(x+3)得3(x+3)-3(x+1)=2(x+1)(x+3)3x+9-3x-3=2(x²+4x+3)3=x²+4x+3x²+4x=0x(x+4)=...