tìm các cặp số nguyên (x,y) biết :x/7+1=1/(y-1)
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x/7 + 1 = 1/(y – 1)=> (x + 7)/x = 1/(y – 1)=> (x +7)(y – 1) = x=> xy -x + 7y – 7 – x = 0=> xy – 2x + 7y – 14 = 14=> x(y – 2) + 7(y – 2) = 14=> (y – 2)(x + 7) = 14x , y in Z => y – 2 ; x + 7 in Ư(14)Ta có bảngy – 2 -14 -7 -2 -1 1 2 7 14x + 7 -1 -2 -7 -14 14 7 2 1y -12 -5 0 1 3 4 9 16x -8 -9 -14 -21 7 0 -5 -6
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x/7 + 1 = 1/(y – 1)=> (x + 7)/x = 1/(y – 1)=> (x +7)(y – 1) = x=> xy -x + 7y – 7 – x = 0=> xy – 2x + 7y – 14 = 14=> x(y – 2) + 7(y – 2) = 14=> (y – 2)(x + 7) = 14x , y in Z => y – 2 ; x + 7 in Ư(14)Ta có bảngy – 2 -14 -7 -2 -1 1 2 7 14x + 7 -1 -2 -7 -14 14 7 2 1y -12 -5 0 1 3 4 9 16x -8 -9 -14 -21 7 0 -5 -6