# Isosceles and equilateral triangles

### Isosceles and equilateral triangles

#### Lessons

• 1.
Find x.
a)

b)

c)

d)

• 2.
In $\triangle DEF$, $\overline {EY}$ is a perpendicular line to $\overline {DF}$ and $Y$ is the midpoint of $\overline {DF}$. Why is $\triangle DEF$ an isosceles triangle? Show your reasoning.