Area of triangles and circles

Cut a rectangle corner to corner and you get two equal triangles. So a triangle is half of a rectangle with the same base and height.

The triangle is half the rectangle:

A = \frac{1}{2} bh

Work through it

Use half of base times height. $\frac{1}{2} (10) (6)$

Calculate. $30$

Square the radius first. $π (3)^{2}$

Calculate. $9 π$

Using the slanted side as the height.

Height is the straight-up distance, at a right angle to the base.

The short version
Triangle:

\frac{1}{2} bh

, with the height straight up from the base. Circle:

π r^{2}

Still stuck? Talk it through with a tutor. The first consultation is free. See our Middle School Math tutoring.