Formula sheet · Grades 9 to 10

Geometry formulas

10 formulas from this course. Each one gives the rule in math, one line on what it means, and a worked example that uses it.

Triangle angle sum

A + B + C = 180^\circ

The three interior angles of any triangle add to 180 degrees.

A + B = 90^\circ

Two angles are complementary when they add to a right angle.

a^2 + b^2 = c^2

In a right triangle the legs squared add to the hypotenuse squared.

A = \pi r^2

The area inside a circle depends on the radius squared.

A = \frac{1}{2}\pi r^2

A semicircle is half a circle, so cut the circle area in half.

C = 2\pi r = \pi d

The distance around a circle, using the radius or the diameter.

V = lwh

The space inside a box, from its length, width and height.

V = \pi r^2 h

Find the area of the circular base, then multiply by the height.

SA = 2(lw + lh + wh)

The total area of all six faces of a box.

V = s^3,\qquad SA = 6s^2

A cube uses only its side length: s cubed for volume and six squares for area.

Practice problems with answers for every Geometry topic.