Question

How do you factor `x^2 + 5x + 4`?

Answer 1

Notice that `5 = 1+4` and `4 = 1*4`, so this can be factored as follows:

`x^2+5x+4 = (x+1)(x+4)`

This is an instance of a general observation that

`(x+a)(x+b) = x^2+(a+b)x+ab`