{4(x+2)=1-5y,3(y+2)=3-2x {2/y+3/x=13,3/y-4/x=3 {x+y=420,30%x+40%y=160*80% 用加减消元法解方程组
问题描述：
{4(x+2)=1-5y,3(y+2)=3-2x {2/y+3/x=13,3/y-4/x=3 {x+y=420,30%x+40%y=160*80% 用加减消元法解方程组
答
{4(x+2)=1-5y,3(y+2)=3-2x4x+8=1-5y4x+5y=-7 (1)3(y+2)=3-2x3y+6=3-2x2x+3y=-3 (2)(2)*2-(1)4x+6y-4x-5y=-6+7y=1x=-3{2/y+3/x=13 (1) 3/y-4/x=3 (2)(1)*4+(2)*38/y+12/x+9/y-12/x=13*4+3*317/y=61y=17/61x=17/33{x+y...