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Find all fractions which can be written simultaneously in the forms (7k - 5)/(5k - 3) and (6l - 1)/(4l - 3), for some integers k,l. |
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Answer» If a fraction is simultaneously in the forms (7k - 5)/(5k - 3) and (6l - 1)/(4l - 3), we must have (7k - 5)/(5k - 3) = (6l - 1)/(4l - 3), This simplies to kl + 8k + l - 6 = 0. We can write this in the form (k + 1)(l + 8) = 14: Now 14 can be factored in 8 ways: 1 x 14, 2 x 7, 7 x 2, 14 x 1, (-1) x (-14), (-2) x (-7),(-7) x (-2) and (-14) x (-1). Thus we get 8 pairs: (k; l) = (13;-7); (6;-6); (1;-1); (0; 6); (-15;-9),(-8;-10); (-3;-15); (-2;-22): These lead respectively to 8 fractions: 43/31, 31/27, 1, 55/39, 5/3, 61/43, 19/13, 13/9. |
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