From the picture, we can see that the three sides of the triangle, *DF*, *FE*, and *ED* are all congruent and therefore have the same length. All the angles are congruent as well. That makes ∆*DEF* an equilateral triangle. How can we figure out the angles of an equilateral triangle? Spoiler alert: They're all equal. We'll call each angle measurement *x*. Since they're all equal and we know all of a triangle's angles add up to 180°, we can set up this equation. *x* + *x* + *x* = 3*x* = 180
*x* = 60
In other words, all the angles in an equilateral triangle have measurements of 60°, including our dear ∠*DFE*. |