Area/Perimeter of basic shapes

On the ACT, students may be asked to calculate the areas of certain common shapes, including triangles, rectangles, and circles. The test will provide students with these formulas, but it’s good to be comfortable with using them before the test, so that questions involving these concepts are just about automatic!

• Triangle

The area of a triangle is = 

12bh where b is the length of the triangle’s base and h is the height of the triangle. For right triangles the height will be equal to the vertical side coming up from the triangle. For non-right triangles, the height is equal to the distance from the base of the triangle to its opposite corner.

Area of Triangle

• Rectangle

The area of a rectangle is equal to the base times the height.

• Circle

The area of a circle is = πr²where r = radius of the circle.

With circles, it’s worth noting that some questions might ask students to use a portion of the area of a circle. This means students just need to use the internal angle measurement of the sector in question to convert the total circle area into the sector area.