Question

classify △def by its angles and by its side lengths.
△def is an acute triangle and .
options for the second dropdown: an equilateral triangle, a scalene triangle

Explanation:

Step1: Analyze side lengths

Check the lengths of all sides of $\triangle DEF$. From the diagram, $DE = 7$ cm, $DF = 7$ cm, and $EF = 7$ cm. So all three sides are equal.

Step2: Classify by side lengths

A triangle with all three sides equal is called an equilateral triangle. Also, since it's equilateral, all angles are equal (each $60^\circ$), which are acute angles, so by angles it's acute, and by sides it's equilateral.

Answer:

an equilateral triangle