Pythagoras Theorem

a² + b² = c²

 Hypotenues = Longest side                                                                             To find the hypotenuse, add the squares of the other sides, then take the square root.            

To find a shorter side, subtract the squares of the other sides, then take the square root.             

If you know two sides of a right-angled triangle, you can find the third like this:

1. square (multiply by itself) the lengths you know
2. add or subtract them
3. find the square root

In any right angled triangle, for any angle:

The sine of the angle = the length of the opposite side
                                       the length of the hypotenuse

The cosine of the angle = the length of the adjacent side
                                           the length of the hypotenuse

The tangent of the angle = the length of the opposite side
                                           the length of the adjacent side

So in shorthand notation:
sin = o/h   cos = a/h   tan = o/a
Often remembered by: soh cah toa