Question

1. select all three isosceles triangles:

Explanation:

Step1: Recall the definition of an isosceles triangle

An isosceles triangle has at least two sides of equal length.

Step2: Analyze each triangle

• Triangle A: No markings indicating equal - length sides. But in a general triangle (without any side - length information), we assume it's a scalene triangle (all sides of different lengths) unless there is a visual or marking clue. Since there are no equal - side markings, it is not isosceles.
• Triangle B: It is a right - angled triangle. A right - angled triangle can be isosceles. In a right - angled isosceles triangle, the two legs (the sides forming the right angle) are equal. Here, there is no indication that the two legs are equal. So, it is a scalene right - angled triangle (not isosceles).
• Triangle C: There are markings indicating two sides are equal. So, it is an isosceles triangle.
• Triangle D: There are markings indicating two sides are equal. So, it is an isosceles triangle.
• Triangle E: No markings indicating equal - length sides. Assume it's a scalene triangle (all sides of different lengths) unless there is a visual or marking clue. Since there are no equal - side markings, it is not isosceles.
• Triangle F: There are markings indicating all three sides are equal. A triangle with all three sides equal (an equilateral triangle) is a special case of an isosceles triangle (because it has at least two sides equal).

Answer:

C, D, F