A right triangle has legs of length 6 and 8. How long is its hypotenuse?
Reveal answer
10 units. Add the squares of the legs to get 100, then take the square root.
6² + 8² = 100
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MathematicsGrade 8
Geometry in practice
Find the missing side of a right triangle.
Meet the hypotenuse
Every right triangle has one 90° angle. The two sides that meet at that angle are the legs. The side across from the right angle is the hypotenuse, the longest side.
Square each leg and add the results. The sum is the square of the hypotenuse.
a² + b² = c²
Explore a 3–4–5 triangle
Leg a measures 3
Square it to get 9. This leg meets the other leg at the right angle.
3² = 9
Leg b measures 4
Square it to get 16. Add that to the first leg’s square.
4² = 16
The hypotenuse measures 5
It sits across from the right angle. Add the two squares and take the square root of 25 to get 5.
3² + 4² = 5²
Check your understanding
Can a triangle with sides 5, 6, and 8 have a right angle?
Reveal answer
No. If it had a right angle, the longest side would be the hypotenuse. Its square is 64, but the other two squares add to 61.
5² + 6² ≠ 8²