数学
七下数学书习题8.4,1题2题答案1.(1){y=2x-7,5x+3y+2z=2,3x-4z=4(2) {4x+9y=12,3y-2z=1,7x+5z=4分之192.(1){4x-9z=17,3x+y+15z=18,x+2y+3z=2(2){2x+4y+3y=9,3x-2y+5z=11,5x-6y+7z=13

2020-05-31

七下数学书习题8.4,1题2题答案
1.(1){y=2x-7,5x+3y+2z=2,3x-4z=4
(2) {4x+9y=12,3y-2z=1,7x+5z=4分之19
2.(1){4x-9z=17,3x+y+15z=18,x+2y+3z=2
(2){2x+4y+3y=9,3x-2y+5z=11,5x-6y+7z=13
优质解答
1题(1)把y=2x-7代入5x+3y+2z=2得11x+2z=23,乘2得22x+4z=46,把它与3x-4z=4相加得x=2,把x=2代入y=2x-7得y=-3,把y=2x-7代入3x-4z=4得z=-1/2.
(2)先把3y-2z=1乘以3得9y-6z=3;4x+9y=12减9y-6z=3得4x+6z=9;把4x+6z=9乘以7得28x+42z=63,把7x+5z=19/4乘以4得28x+20z=19;两式相加得22z=44,解得z=2分别代入解得x=-3/4,y=5/3.
1题(1)把y=2x-7代入5x+3y+2z=2得11x+2z=23,乘2得22x+4z=46,把它与3x-4z=4相加得x=2,把x=2代入y=2x-7得y=-3,把y=2x-7代入3x-4z=4得z=-1/2.
(2)先把3y-2z=1乘以3得9y-6z=3;4x+9y=12减9y-6z=3得4x+6z=9;把4x+6z=9乘以7得28x+42z=63,把7x+5z=19/4乘以4得28x+20z=19;两式相加得22z=44,解得z=2分别代入解得x=-3/4,y=5/3.
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