For those of you who know how to solve absolute value inequalities, here is how they also mean something like “numbers between 8 and 14.”
Category: Math Analysis
A moderately difficult trig identity: prove 
Here’s one of the things about complex numbers which is easier if you know it so well you don’t have to think about it: the formula for sin x. Nice and easy. Assumes you already know Euler’s formula, eix = cos x + i sin x.
Assuming you know the basics (tan=sin/cos, etc), here are strategies and examples for proving simple trig identities.
Gauss was just ten years old when he discovered how to quickly add up a long series of numbers. Here I tell the story of how he outwitted his teacher and I also walk you through a mathematical proof.