Question

已知x^2+y=8x+6y+25=0,求2x+3y的值

Answer 1

x^2+y^2+8x+6y+25=(x+4)^2+(y+3)^2=0.

因为(x+4)^2>=0、(y+3)^2>=0,所以(x+4)^2=0、(y+3)^2=0,即x=-4、y=-3.

2x+3y=-8-9=-17.