Expert: Bobby Soltani - 2/12/2006

Question
x^2-4x-77

Answer
Hi,

x^2 - 4x - 77

77 can be broken into 7*11, so we write

(x   7)(x   11)

We need to determine whether a plus or minus sign goes in each parentheses.  Since 77 is negative, we know that the signs must be opposite.

(x + 7)(x - 11)

Let's try that.

x^2 + 7x - 11x - 77

x^2 - 4x - 77

It works.  Let me know if you have any questions.

Bobby