What is the formula for the area of an equilateral triangle?
Understand the Problem
The question is asking for the mathematical formula that calculates the area of an equilateral triangle, which is a triangle with all three sides of equal length.
Answer
\frac{\sqrt{3}}{4}a^2
Answer for screen readers
The final formula for the area of an equilateral triangle with side length $a$ is $\frac{\sqrt{3}}{4}a^2$
Steps to Solve

Identify the formula for the area of an equilateral triangle
For an equilateral triangle with side length $a$, the formula for the area $A$ is derived using the formula for the area of a general triangle and some geometric properties.

Use the formula for the area of a general triangle
The area $A$ of a triangle is given by
$$A = \frac{1}{2} \times base \times height$$
For an equilateral triangle, all sides are equal and the height can be calculated using the Pythagorean theorem.

Calculate the height of the equilateral triangle
Split the equilateral triangle into two rightangled triangles. Each of these right triangles has a base of $\frac{a}{2}$ and a hypotenuse of $a$. Use the Pythagorean theorem to find the height $h$:
$$a^2 = \left(\frac{a}{2}\right)^2 + h^2$$
Solving for $h$,
$$h^2 = a^2  \left(\frac{a}{2}\right)^2$$
$$h^2 = a^2  \frac{a^2}{4}$$
$$h^2 = \frac{3a^2}{4}$$
$$h = \frac{\sqrt{3}}{2}a$$

Substitute the height into the area formula
Substitute the height calculated into the general area formula to get the area of the equilateral triangle:
$$A = \frac{1}{2} \times a \times \frac{\sqrt{3}}{2}a$$
Simplifying,
$$A = \frac{\sqrt{3}}{4}a^2$$
The final formula for the area of an equilateral triangle with side length $a$ is $\frac{\sqrt{3}}{4}a^2$
More Information
This formula helps quickly find the area of an equilateral triangle using just the side length. It's derived from the properties of the equilateral triangle.
Tips
Common mistakes include forgetting to correctly apply the Pythagorean theorem or substituting the height back into the area formula. Doublecheck each step to avoid these errors.