用代入法解下列方程组1题2x-y=6,x+2y=-2.2题x+y=420,30%x+40%y=160*80%
问题描述:
用代入法解下列方程组1题2x-y=6,x+2y=-2.2题x+y=420,30%x+40%y=160*80%
答
1:{2X-Y=6 (1) (1)变(3):2X-6=Y (3)X+2Y=-2.2 (2) (3)代入(2)得:X+2(2X-6)=-2.2 X+4X-12=-2.25X=-2.2+12 5X=9.8 X=1.96 将X=1.96代入(1)得:2×1.96-Y=6 Y=3.92-6 Y=-2.08X=1.96 Y=-2.082:{X+Y=420 (1) (...