Right Angled

1 angle is a right angle which is 90 degrees
No lines of symmetry

Hypotenuse

The longest side is called the hypotenuse

Pythagoras Theorem

This only works for right angled triangles
a2 + b2 = c2
Using the length of 2 sides you can calculate the length of the third side.

Basic Trigonometry

More Details
Calculating the length of the sides
Calculating the size of the angles - using the inverse functions

SOH
sin x = opposite / hypotenuse

CAH
cos x = adjacent / hypotenuse

TOA
tan x = opposite / adjacent