Answer:
Option 1 is correct.
Explanation:
To find: Correct definition of Isosceles triangle
Isosceles triangles are the triangle whose 2 side are equal.
Option 1:
A triangle that has at least two congruent side.
congruent means equal.
Here, triangle has at least 2 equal side which is of isosceles triangle.
Thus, this option is correct.
Option 2:
A triangle in which no 2 sides are congruent.
Here it is said that no two sides are equal this contradict the fact of isosceles having two equal side.
Thus this option incorrect.
Option 3:
A triangle that has three congruent sides.
Here All 3 sides of triangle are equal. this implies triangle is an equilateral triangle not the isosceles triangle.
Thus, this option is incorrect.
Therefore, Option 1 is correct.