The question asks to name the missing side $x$ in $\triangle ABC$, with the reference angle at $A$. Here's how to approach this:

1. In a right triangle, the sides are named relative to the reference angle:

   • Opposite: The side opposite the reference angle.
   • Adjacent: The side next to the reference angle that is not the hypotenuse.
   • Hypotenuse: The side opposite the right angle (the longest side).

2. Observing the diagram:

   • The hypotenuse is labeled as 11 (side $AB$).
   • The side $x$ is directly opposite the reference angle $A$, making it the opposite side.

Correct answer:

Opposite

Would you like a detailed explanation of how to classify triangle sides or more practice problems?

Related Questions:

1. What is the definition of the adjacent side in a right triangle?
2. How do you calculate the missing side length in a right triangle using trigonometric ratios?
3. How do you identify the hypotenuse in any right triangle?
4. Why is the hypotenuse always the longest side in a right triangle?
5. Can the adjacent and opposite sides ever have the same length in a right triangle?

Tip:

Remember, labeling sides relative to a reference angle is essential in using trigonometric functions like sine, cosine, and tangent.