How do you solve the inequality x²+x>1. I can not remember how to factor it. It doesnt make sense to me how you can have a single x and a negative 1

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- Jan 15th 2007, 08:29 PMmsdonnellyinequality question
How do you solve the inequality x²+x>1. I can not remember how to factor it. It doesnt make sense to me how you can have a single x and a negative 1

- Jan 15th 2007, 08:32 PMmsdonnellyinequality question
x²+x>1. I can not remmeber how to solve this it doesnt make sense to me how you can have a single x and a negative 1. x(x+1)-1 ???

- Jan 15th 2007, 09:13 PMCaptainBlack
- Jan 16th 2007, 01:33 AMearboth
- Jan 16th 2007, 04:07 AMtopsquark

(Take a look at the graph I have attached.)

We are looking for the portion of the x-axis where the graph is above the x-axis.

We do this algebraically by the following process.

Solve

according to the quadratic formula.

Now break the x-axis into three parts:

We want to test the inequality on each of these intervals. The idea is to pick the easiest number in the interval to do the test on, so for example pick -100000000000000 in the first interval, pick 0 in the second, and pick 100000000000000 in the last interval. (Or any other numbers you like.)

: Check!

: Nope!

: Check!

So the solution set is .

-Dan