几个两元一次方程,0.5x+0.7y=35x+0.4y=405x+y=2x-3y=43x-2y=12x+3y=-7x/3

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  • 5X+7Y=350X=40-0.4Y5*(40-0.4Y)+7Y=350200-2Y+7Y=3505Y=150Y=30X=40-0.4*30=2815X+3Y=6 X-3Y=416X=10 X=0.625 Y=2-5*0.625=-1.1253. 6X-4Y=2 6X+9Y=-21 13Y=-23 Y=-23/13 X=(1-2*23/13)/3=-11/134. 4X-3Y=12 3X-4Y=2 所以X+Y=10 即7X+7Y=70 7X-7Y=14 14X=84 X=6 Y=45. 0.3X-Y=1 0.4X-Y=38 0.1X=37 X=370 Y=0.3*370-1=1106. 4X-15Y=3 X=(3+15Y)/4 代入6X-25Y-23=-16中 (18+90Y)/4-25Y=7 18+90Y-100Y=28 -10Y=10 Y=-1 X={3+15*(-1)}/4=-3