Exercise 18 Page 612

Let's start by drawing a side that is $1.25$ inches using a straightedge.

Next, we use a compass to draw an arc with center $A$ and a radius of $1.25$ inches.

Using the compass again, we will draw one more arc with center $B$ and radius of $1.25$ inches. The intersection with the other arc, we label $C.$

By drawing $\overline{AC}$ and $\overline{BC},$ we have constructed an equilateral triangle with a side length of $1.25$ inches.