(This lesson also appears in the Algebra I curriculum.
If you studied it there, then just quickly review, and move on to the next section!)
A 90° angle is called a right angle.
A right triangle is a triangle with a 90° angle.
In a right triangle, the side opposite the 90° angle is called the hypotenuse
and the remaining two sides are called the legs.
The angles in any triangle add up to 180°.
In any triangle, the longest side is opposite the largest angle,
and the shortest side is opposite the smallest angle.
Thus, in a right triangle, the hypotenuse is always the longest side.
The Pythagorean Theorem gives a beautiful relationship between the lengths of the sides in a
right triangle:
the sum of the squares of the shorter sides is equal to the square of the hypotenuse.
Furthermore, if a triangle has this kind of relationship between the lengths of its
sides, then it must be a right triangle!
THE PYTHAGOREAN THEOREM Let [beautiful math coming... please be patient]$\,\,T\,\,$ be a triangle with sides of lengths [beautiful math coming... please be patient]$a$, [beautiful math coming... please be patient]$b$, and [beautiful math coming... please be patient]$c$, where [beautiful math coming... please be patient]$\,c\,$ is the longest side (if there is a longest side). Then, 

6810  ( k = 2 ) 
91215  ( k = 3 ) 
1.522.5  ( k = 0.5 ) 
3π4π5π  ( k = π ) 
On this exercise, you will not key in your answer. However, you can check to see if your answer is correct. 
PROBLEM TYPES:
