I thought I'd teach myself some A-Level Maths at home and I'm stuck on a problem I got from mymaths. Problem is mymaths don't bother providing answers, and the tutorial section didn't show me how to solve it and I kept getting the answer wrong.
$18< x^2 + 3x<40$
I had to solve this. I decided to do them as separate inequalities,
And after factorizing and sketching a rough graph I got the respective values:
The problem is that's as far as I got, and when I put any of the above as my answer, I still got it wrong. What is the answer and how do I get it? Have I gone wrong anywhere?