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發問:

唔識做； 耀答案 1) x+y=4 x+y=2 2)x-y=1 2x+3y=7 3)5x+2y=28 3x+5y=51

最佳解答:

1) x + y = 4 ...(1) x - y = 2 ... (2) (1), x = 4 - y ... (3), Put(3) into (2), 4 - y - y = 2 4 - 2y = 2 2y = 2 y = 1, x = 4 - 1 = 3 So, x = 3, y = 1. 2) 2x + 3y = 7 ...(1) x - y = 1 ...(2) (2), x = y + 1 ... (3), Put(3) into (1), 2(y + 1) + 3y = 7 5y + 2 = 7 y = 1, x = 1 + 1 = 2, So, x = 2, y = 1. 3) 5x + 2y = 28 ... (1), 3x + 5y = 51 ... (2), (2), x = (51 - 5y) / 3 ... (3) Put(3) to (1), 5(51 - 5y) / 3 + 2y = 28 255 - 25y + 6y = 84 -19y = -171 y = 9, x = (51 - 45) / 3 = 3, Som x = 3, y = 9

其他解答:

x+y=4 x-y=2 _______ From1: x=4-y-----------3 Sub 3 into 2 : 4-y-y=2 -2y+4=2 -2y=-2 y=1 Put y=1 into 3: x=3 2010-09-30 17:48:31 補充： x-y=1-----------------1 2x+3y=7--------------2 ___________ From1: x=1+y--------3 Sub. 3 into 2: 2+2y+3y=7 5y=5 y=1 Put y=1 into 3: x=2 2010-09-30 17:53:44 補充： 5x+2y=28-------1 3x+5y=51--------2 _______________ From1: y=(28-5x)/2----------3 Sub 3 into 2: 3x+5((28-5x)/2)=51 6x+140-25x=102 x=2 Put x=2 into 3: y=9
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