Answer:
3. A quadrilateral with each side length 4 cm
Step-by-step explanation:
We need to understand what is a unique polygon?
<em>It means all regular polygons with the same number of sides are similar.</em>
1.A triangle with angles 30 degrees, 60 degrees, and 90 degrees
It is an right triangle, so the 3 sides are not simillar, so it is wrong
2. A triangle with side lengths 5 cm, 4 cm, and 3 cm
It is a triangle with the 3 sides are not simillar, so it is wrong
3. A quadrilateral with each side length 4 cm
It is an square with the 4 sides are simillar, so it is true
4. A triangle with side lengths 7 cm and 8 cm and a 40-degree angle
It is a triangle with the 3 sides are not simillar, so it is wrong
Hence, we choose 3.
