Question 1074226
If you are in algebra studying inequalities, then

https://www.youtube.com/watch?annotation_id=annotation_2661305721&feature=iv&src_vid=0VVQYOMRlkQ&v=DPtM2aVuTlI

https://www.youtube.com/watch?v=8FCV2-EjgXg

But if you're in calculus studying increasing and decreasing
functions or concavity

https://www.youtube.com/watch?v=c1N8zyVhWxM