The Pythagorean theorem, also known as Pythagoras' theorem, is an important theorem related to right-angled triangles. Let's consider the right triangle depicted below.



The theorem can be written as \begin{align*} {\color{red}{c}}^{\color{black}{2}} = {\color{blue}{a}}^{\color{black}{2}} + {\color{blue}{b}}^{\color{black}{2}}, \end{align*}

where

  • \color{red}c is the length of the longest side, which is called the hypotenuse, and

  • \color{blue}a and \color{blue}b are the lengths of the two other sides, which are called the legs.

FLAG

Find the length of the hypotenuse in the triangle below.


EXPLANATION

The given lengths are the legs of the right triangle, so let a=8 and b=6. According to the Pythagorean theorem, we obtain

\begin{align*} c^2 &= a^2 + b^2 \\[2pt] c &= \sqrt{a^2 + b^2}. \end{align*}

Substituting in the values for a and b gives us

\begin{align*} c &= \sqrt{(8)^2 + (6)^2} \\[2pt] &= \sqrt{64 + 36} \\[2pt] &= \sqrt{100} \\[2pt] &= 10. \end{align*}

Watch out! When taking the square root of c^2 we only take the positive value. The reason for this is that we cannot have a negative length.

FLAG

Find the length of the hypotenuse in the triangle above.

a
$4$
b
$1 + \sqrt{3}$
c
$2$
d
$2\sqrt{3}$
e
$3$

Find the length of the hypotenuse in the triangle above.

a
$12\,\textrm{cm}$
b
$14\,\textrm{cm}$
c
$10\,\textrm{cm}$
d
$7\,\textrm{cm}$
e
$5\,\textrm{cm}$

A right triangle has legs of length 5 and 12. Calculate the length of its hypotenuse.

EXPLANATION

Let a=5, b=12, and c be the length of the hypotenuse. According to the Pythagorean theorem, we obtain

\begin{align*} c^2 &= a^2 + b^2 \\[2pt] c &= \sqrt{a^2 + b^2}. \end{align*}

Substituting in the values for a and b gives us

\begin{align} c &= \sqrt{(5)^2 + (12)^2} \\[2pt] &= \sqrt{25 + 144} \\[2pt] &= \sqrt{169} \\[2pt] &= 13. \end{align}

FLAG

A right triangle has legs of length $24$ and $10.$ Calculate the length of its hypotenuse.

a
$32$
b
$24$
c
$26$
d
$34$
e
$36$

A right triangle has legs of length $7$ and $24.$ Calculate the length of its hypotenuse.

a
$25$
b
$33$
c
$31$
d
$35$
e
$29$

What is the length of a in the triangle shown below?


EXPLANATION

Here, we know the lengths of the hypotenuse and one leg, so let b=9 and c=15. We need to find a, the length of the other leg.

According to the Pythagorean theorem, we obtain

\begin{align} c^2 &= a^2 + b^2 \\[2pt] a^2 &= c^2 - b^2 \\[2pt] a &= \sqrt{c^2 - b^2}. \end{align}

Substituting in the values for b and c gives us \begin{align} a &= \sqrt{(15)^2 - (9)^2} \\[2pt] &= \sqrt{225 - 81} \\[2pt] &= \sqrt{144} \\[2pt] &= 12. \end{align}

FLAG

What is the length of $a$ in the triangle shown above?

a
$\sqrt{65}$
b
$\sqrt{5}$
c
$\sqrt{13}$
d
$13$
e
$10$

What is the length of $a$ in the triangle shown above?

a
$16$
b
$10$
c
$14$
d
$15$
e
$12$
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