1. ## [SOLVED] Factor 4x^2+31x-8

How do you factor 4x^2+31x-8?

~calligrapher~

2. Originally Posted by calligrapher
How do you factor 4x^2+31x-8?

~calligrapher~
$\displaystyle (4x-1)(x+8)$

3. Here's a good method for solving quadratics like these when $\displaystyle a > 1$

Multiply a and c and find the factors of there product whose sum is b. In this case $\displaystyle 4 \cdot -8 = -32$ and $\displaystyle 32 = 32 \cdot -1$ and $\displaystyle 32 + (-1) = 31$ These are what numbers you try to get when you foil.

So it will factor to
$\displaystyle (4x - 1)(x + 8)$

and $\displaystyle x \in \{\frac{1}{4}, -8\}$

4. Originally Posted by SnipedYou
Here's a good method for solving quadratics like these when $\displaystyle a > 1$

Multiply a and c and find the factors of there product whose sum is b. In this case $\displaystyle 4 \cdot -8 = -32$ and $\displaystyle 32 = 32 \cdot -1$ and $\displaystyle 32 + (-1) = 31$ These are what numbers you try to get when you foil.

So it will factor to
$\displaystyle (4x - 1)(x + 8)$

and $\displaystyle x \in \{\frac{1}{4}, -8\}$
How can it have a solution when it isn't an equation?

-Dan