Question

which triangle is a right triangle?

Explanation:

Step1: Define right triangle

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

Step2: Check each triangle

• Triangle 1: Angles $45^\circ, 55^\circ, 80^\circ$ (no $90^\circ$)
• Triangle 2: Angles $60^\circ, 60^\circ, 60^\circ$ (no $90^\circ$)
• Triangle 3: Angles $35^\circ, 35^\circ, 110^\circ$ (no $90^\circ$)
• Triangle 4: Angles $60^\circ, 30^\circ, 90^\circ$ (has $90^\circ$)

Answer:

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