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
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![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](/uploads/image/z/1342825-25-5.jpg?t=%E4%B8%83%E4%B8%8B%E6%95%B0%E5%AD%A6%E4%B9%A6%E4%B9%A0%E9%A2%988.4%2C1%E9%A2%982%E9%A2%98%E7%AD%94%E6%A1%881.%EF%BC%881%EF%BC%89%7By%3D2x-7%2C5x%2B3y%2B2z%3D2%2C3x-4z%3D4%282%29+%7B4x%2B9y%3D12%2C3y-2z%3D1%2C7x%2B5z%3D4%E5%88%86%E4%B9%8B192.%EF%BC%881%EF%BC%89%7B4x-9z%3D17%2C3x%2By%2B15z%3D18%2Cx%2B2y%2B3z%3D2%282%29%7B2x%2B4y%2B3y%3D9%2C3x-2y%2B5z%3D11%2C5x-6y%2B7z%3D13)
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
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
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
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.
一步一步来(1)把y=2x-7代入下一个式子得11x+2z=23 3x-4z=4 z=2-11x/2在代入得x=8/25带回上式得z=-19/25那么y=-6.36
下面用相同的方法做
第一题(1)y=2x-7 z=(3x-4)/4 代入 5x+3*(2x-7)+2*(3x-4)/4=2解得x=2 y=-3 z=0.5
(2)3y=(12-4x)/3 z=(4-7x)/5 代入 (12-4x)/3-2*(19/4-7x)/5=1解得x=-3/4,y=5/3,z=2
第二天(1)y=18-3x-15z=1-1/2x-3/2z 化简得34=5x+27z ,9z=4x-17 解得x=5,z=1/3 代入可得y=-2