To find the unknown side length in the right triangle using the Pythagorean Theorem, we can use the formula:
\[ a^2 + b^2 = c^2 \]
Where:
- \(a\) and \(b\) are the lengths of the two legs of the triangle,
- \(c\) is the length of the hypotenuse.
In this case:
- The base \(a = 3\),
- The hypotenuse \(c = 15\),
- We need to find the perpendicular side, which we'll call \(b\).
Plugging in the values we have into the Pythagorean theorem gives us:
\[ 3^2 + b^2 = 15^2 \]
Calculating the squares:
\[ 9 + b^2 = 225 \]
Next, we subtract 9 from both sides:
\[ b^2 = 225 - 9 \]
\[ b^2 = 216 \]
Now, we take the square root of both sides to solve for \(b\):
\[ b = \sqrt{216} \]
Calculating the square root:
\[ b \approx 14.7 \]
Rounding to the nearest tenth, we conclude that the length of the unknown side is approximately 14.7.
Thus, the correct response is:
14.7