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p^2-2pq+q^2-25

49-x^2+2xy-y^2

16x^4y^4-x^4+2x^2y^2-y^4

(p-q) ^2-25 = (p-q-5) (p-q+5)

49-x^2+2xy-y^2=7^2 - (x^2-2xy+y^2) = 7^2 - (x-y) ^2 = (7-x+y) (7+x-y)

16x^4y^4-x^4+2x^2y^2-y^4 = (4x^2y^2) ^2 - (x^4-2x^2y^2+y^4) = (4x^2y^2) ^2 - (x^2-y^2) ^2=

(4x^2y^2-x^2+y^2) (4x^2y^2+x^2-y^2)