Trigono + Metry = Triangle + Measure

Triangle is any figure that has 3 angles. Angle is the measure of rotation of a line about a fixed point.

Trigonometry is used in many areas such as the science of seismology, designing electric circuits, describing the state of an atom, predicting the heights of tides in the ocean, analyzing a musical tone and in many other areas

For better understanding, click on the below link : 

https://www.youtube.com/watch?v=HdB63fiud6I&list=PLCzaIJYXP5YdD-nMkUNAKq3PAeBDVV23S&index=17