x^2+9x/x^2+3x加上x^2-9/x^2+6x+9 =x(x+9)/x(x+3)+(x-3)(x+3)/(x+3)²=(x+9)/(x+3)+(x-3)/(x+3)=(x+9+x-3)/(x+3)=2解方程：2x/2x-5加上5/5+2x=12x(2x+5)+5(2x-5)=4x²-254x²+10x+10x-25=4x²-2520x...