Bianca calculated the height of the equilateral triangle with side lengths of 10.

tangent (30) = StartFraction 5 Over h EndFraction An equilateral triangle with side lengths of 10 is shown. A bisector is drawn to split the side into 2 equal parts and splits the angle into 2 30 degree segments.
Then, she used the formula for area of a triangle to approximate its area, as shown below.

A = one-half b h. = one-half (10) (8.7). = 43.5 units squared.

Calculate the area of the equilateral triangle using the formula for area of a regular polygon, and compare it to Bianca’s answer.

The apothem, rounded to the nearest tenth, is
units.

The perimeter of the equilateral triangle is
units.

Therefore, the area of the equilateral triangle is
, or approximately 43.5 units2.

The calculated areas are
.