Answer 2: The original formula = 15 (2x-y) 2-22 (2x-y)+8.

=( 10x-5y-4)(6x-3y-2)

Answer 3: the original formula = (x-3y+m) (x+y+n)

Expand x 2-2xy-3y 2+(m+n) x+(m-3n) y+Mn.

So m+n=3 m-3n=-5.

The solution is m= 1 n=2, so k = Mn = 2.

When k is 2, it can be decomposed into (x-3y+ 1)(x+y+2).

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