Question

How do you factor 3x^2+2x-28

Answer 1

When you get a quadratic with an x^2 coefficient greater than one you multiply the constant by the x^2 coefficient to get 3 times 28, or 84.

Now you want to factorise 84 into two so that the factors add to the coefficient of x, or 2 in this case.

The way to find these two factors is to divide 84 by 2, 3, 4, and so on until you see the two factors add to 2.

Let's try it: 2 times 42, 3 times28, 4 times21, 5 doesn't go, 6 times 14, 7 times 12,keep going.....until the two factors have a difference of 2.

OOPS! There's something wrong. It doesn't factorise in integers.

Are you sure you have written the quadratic correctly?