Pythagoras Theorem applies ONLY to Right Angles Triangles and it connect the two short sides to the long (hypotenuse) side:
Step 1: Draw a neat diagram. Make sure you draw in the right angle.
Step 2: Label the side that the right angle is pointing at (ie the longest of the 3 sides) as H for Hypotenuse
Step 3: Label the other 2 sides as a and as b (NB. It doesn’t matter which way round you put the a and b labels)
Eg:

Step 4: Read the question carefully, is it asking you to find the H side or is it asking you to find an a or a b side?
Step5: Decide do you prefer to do the question using the Arithmetic (method 1) or by the Taking the FIS (method 2)?
Arithmetic (method 1):
In this method you have to remember only 2 things:
1. To find the H side you need to ADD
2. To find either the a or the b side you need to SUBTRACT
eg
To find the H side, Square the a side
Square the b side
ADD the answers
Square Root

a side:
b side:
total:
answer:
eg
To find either the a (or the b) side, Square the H side
Square the b side (or the a side)
SUBTRACT the answers
Square Root

H side:
b side:
total:
answer:
Taking the FIS (method 2):
In this method you have to remember only the Formula:
eg
To find the H side simply take the FIS

eg
To find either the a (or the b) side simply take the FIS
