Which statement correctly describes an isosceles triangle?

• A. A triangle with all sides equal
• B. A triangle with no congruent sides
• C. A triangle with at least two congruent sides
• D. A triangle with one angle of 90 degrees

Answer: (C)

Isosceles triangles are defined by having two equal sides. That makes the statement describing an isosceles triangle exactly: a triangle with at least two congruent sides. When two sides are equal, the angles opposite those sides are also equal, which is a helpful property to remember. It’s also worth noting that equilateral triangles—where all three sides are equal—still fit this definition because they certainly have at least two equal sides. A triangle with no congruent sides is scalene, not isosceles. A triangle with a 90-degree angle is a right triangle, and while it can be isosceles if two legs are equal, just having a right angle doesn’t define an isosceles triangle by itself.