Question

which triangle is a right triangle?

Explanation:

Step1: Define right triangle

A right triangle has one $90^\circ$ angle.

Step2: Check each triangle

1. Top-left: Has a $90^\circ$ angle. Sum: $60^\circ+30^\circ+90^\circ=180^\circ$
2. Top-right: $45^\circ+80^\circ+55^\circ=180^\circ$, no $90^\circ$ angle.
3. Bottom-left: $35^\circ+35^\circ+110^\circ=180^\circ$, no $90^\circ$ angle.
4. Bottom-right: $60^\circ+60^\circ+60^\circ=180^\circ$, no $90^\circ$ angle.

Answer:

The triangle with angles $60^\circ$, $30^\circ$, and $90^\circ$ (top-left triangle) is a right triangle.