Gene G. answered • 05/21/19
Retired Electrical Engineer Helping People Understand Algebra
Since -40 is negative, one factor will be positive and one negative.
Just make a table of possible factors and look at their sums. When you find a pair that adds up to -9, you're done.
-1, 40 sum 39 (or 1, -40, sum -39)
-2, 20 sum 38 (or -38)
-4, 10 sum 6 (or -6)
-8, 5 sum +/- 3
-10,4 sum -6 - We already have this one. Anything from here out will be a repeat.
It looks like you're trying to factor a quadratic, but this one doesn't factor nicely. You'll have to use the quadratic formula to solve for x.
x = [-b +/- sqrt (b2-4ac)] / [2a]
a,b and c are the coefficients in the quadratic: ax2 + bc + c = 0
plug in the values of a, b, and c then simplify it to just a number value. There will be two answers, one the positive square root and one for the negative square root.
