Question

方程组{ax+2y=7,2x-b=5的解x、 y互为相反数,且a为b的3倍,求a、b的值

Answer 1

x、 y互为相反数,即：y=-x,代入

2x-b=5 2x=5+b x=(5+b)/2

3b*x+2(-x)=(3b-2)x=(3b-2)(5+b)/2=7 3b^2+13b-24=0

b=(-13+/-√457)/6

a=(-13+/-√457)/2