What is the factor for the quadratic x2 - x - 648 equals 0?

(x2-x-648)=0

We need two numbers that differ by 1 and whose product is 648.

The factors of 648 are:

1 2 3 4 6 8 9 12 18 24 27 36 54 72 81 108 162 216 324 648

There are no such numbers, therefor, this quadratic cannot be factored.

You may find these links handy:

http://www.1728.com/quadratc.htm

http://www.Apples4theteacher.com/prime-factors.html