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

2 Answers
Sep 21, 2015

Answer:

#(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

Answer:

#(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.