Calculate Circle Area: Finding the Area When Diameter = 13

The area formula $A = \pi r^2$ specifically requires the radius, not diameter. Using diameter gives you an answer that's four times too big because you're squaring a number that's twice as large!

Think of it this way: the diameter goes all the way across the circle through the center, while the radius only goes from center to edge. So radius is always half the distance!

You can calculate it! $6.5^2 = 6.5 \times 6.5 = 42.25$. This gives you the cleaner answer 42.25π instead of $(6.5)^2\pi$.

The process stays the same! Always divide the diameter by 2 to get the radius, then square that radius and multiply by π. For example: diameter 8 → radius 4 → area 16π.

Leaving answers as 42.25π is more exact than using π ≈ 3.14159. Many geometry problems expect answers in terms of π unless specifically asked for a decimal approximation.