Some signs would have helped answerers but for what its worth 7 & 8 are factors of 56 which differ by 1 so how about:
(y - 7x)(y + 8x) which are the factors of y2 + xy - 56x2 or
(y + 7x)(y - 8x) which are the factors of y2 - xy - 56x2.
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2(x - y)(x + y)(x2 - xy + y2)(x2 + xy + y2)
y4 - 256 = (y2 - 16)(y2 + 16) = (y - 4)(y + 4)(y2 + 16)
x2-y2=(x-y)(x+y) which is a well known identity.
(y + 3)(y - 10)
If that's y2, the answer is (y - 5)(y + 3)