Applying Formulas in Geometry:

You will have access to a page of formulas during the test. Be sure you know which formula to use for different questions and that you know the abbreviations in the formulas.

Triangles and rectangles: compute area, perimeter, and side lengths

Lengths of sides are usually given, or you can figure them out by using other information given.

Perimeter is the total length of all of the sides of a shape. Just add them together.

Area is the measurement of the space covered by a shape and is written in square units, such as square feet or ft2


For a rectangle or square, multiply base x height. (b x h)

For a triangle, do the same and divide in half. (½(b x h)

Circles: Compute area, circumference, radius, and diameter.

When working with circles, you will need to use a number called Pi which is 3.14 and the symbol for Pi is π. You will also need to work with these terms and formulas:

The radius ( r ) is the length of a line from the center point to any point on the circle.

The diameter (d) is the length of a line between any 2 points on the circle that goes through the center point. It is always 2 x radius (r).

The circumference is the distance around the circle. It is found using this formula: 2 x π x r or 2πr

The area of a circle is: πxr2

or πr2

Polygons: Compute area and side lengths. A polygon is a closed, flat shape, with 3 or more sides.

Composite figures: Compute perimeter and area. Composite shapes are figures made of 2 or more attached shapes. In order to find the perimeter and area, you would have to consider all of the outside sides or inside space of all of the shapes in the figure. These composite shapes may include circles.

Pythagorean theorem

This formula only works for a triangle with a 90° angle (right triangle). The hypotenuse is the side opposite the right angle. In this formula, c is the hypotenuse and a and b are the other sides, called the legs. The theorem is a2

+ b2 = c2


Volume, surface area, and other dimensions of 3 dimensional figures: rectangular prisms, cylinders, right prisms, right pyramids, spheres, and 3-D composite geometric figures. Surface area is the total area measurement of all of the outside surfaces of the 3-D shape.