17 yards. The fence that enclose Sondra's backyard is a right triangle whose sides measuring 8 yards, 15 yards and 17 yards respectively.
The key to solve this problem is using the Pythagorean Theorem that dictates; In every right triangle the square of the hypotenuse is equal to the sum of the squares of the legs and the equation hypotenuse²=leg1²+leg2².
For this problem we know the measuring of two side, which mean that we can apply Pythagorean Theorem equation as follow:
Let's say that one of the side is a = 8yards, and the other side is b = 15yards. So, we want to know how long the third side c long.
Applying the Pythagorean Theorem:
![c^(2) =a^(2)+b^(2) \\c=\sqrt{a^(2)+b^(2)}](https://img.qammunity.org/2020/formulas/mathematics/high-school/4ztwmfbq2x5l1wciopxcy1risu46ez2r23.png)
Substituting the values of the sides a and b:
![c=\sqrt{(8yards)^(2)+(15yards)^(2)}\\c=\sqrt{64yards^(2)+225yards^(2)}\\c=\sqrt{289yards^(2)}\\c=17yards](https://img.qammunity.org/2020/formulas/mathematics/high-school/ds8r8ma2w2rxkyyss7nvhduebf1sm07k4a.png)