Question

How do you factor `3x²-12xy-63y²`?

Answer 1

Given `3x^2-12xy-63y^2`

Extract the obvious common numeric factor `3`
`color(white)("XXXX")` `=3(x^2-4xy-21)`

`21` can be factored as `3xx7` and `3-7 = -4`
so
`color(white)("XXXX")` `=3(x+3)(x-7)`