Which statement correctly describes an isosceles triangle?

Which statement correctly describes an isosceles triangle?

• A. All sides are different.
• B. It has a right angle.
• C. Two sides are congruent.
• D. All angles are equal.

Answer: (C)

Isosceles triangles have two sides of equal length. That makes the statement “Two sides are congruent” the defining description of an isosceles triangle. Because two sides are equal, the angles opposite those sides are equal as well, giving the usual base-angle equality. If all three sides were different, it would be a scalene triangle. A right angle isn’t required—an isosceles triangle can be non-right, though it can be right-angled if the equal sides meet at the right angle. All angles being equal would describe an equilateral triangle, which requires all three sides to be equal. So the statement about two sides being congruent is the correct description.

Isosceles triangles have two sides of equal length. That makes the statement “Two sides are congruent” the defining description of an isosceles triangle. Because two sides are equal, the angles opposite those sides are equal as well, giving the usual base-angle equality.

If all three sides were different, it would be a scalene triangle. A right angle isn’t required—an isosceles triangle can be non-right, though it can be right-angled if the equal sides meet at the right angle. All angles being equal would describe an equilateral triangle, which requires all three sides to be equal.

So the statement about two sides being congruent is the correct description.