How do you factor x^2 + x - 42?

2 Answers
Sep 21, 2015

(x+7)(x-6)

Explanation:

Factoring quadratic equations is usually a trial and error thing (at least for me). Here's how I answered it in my head.

First, I thought of the factors of x^2. The only possible ones are x and x.

Next, I thought: What two factors of -42 are equal to 1 (since that is the coefficient of x) when added?
The two numbers that I thought of were -6 and 7, since -6+7=1.

Therefore, my factors are (x+7) and (x-6).

You can try double-checking this by multiplying (x+7) and (x-6).

If you don't like "guessing" the factors, you can also use the quadratic formula for that. Though I suggest you don't since it is time consuming.
x=(-b±sqrt(b^2-4ac))/(2a)

Sep 21, 2015

(x-6)(x+7)

Explanation:

Cross factorise it! It's a little hard to explain so you should watch a video which would help you understand even better.

To check:
Expand the brackets! You will get the same answer.