6m^2 - 13mn - 5n^2 =
= 6m^2 - 15mn + 2mn - 5n^2 =
= 3m (2m - 5n) + n (2m - 5n) =
= (2m - 5n)(3m + n)
357, 375, 537, 573, 735, 753,
335, 353, 533,
337, 373, 733,
553, 535, 355,
557, 575, 755,
775, 757, 577,
773, 737, 377
48n/16n-1*3n-3 = 144n^2/16n-1 - 3 = 144n^2-3(16n-1)/16n-1 = 144n^2-48n+3/16n-1
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