How to Figure the Dimensions of Various Shapes

A Circle

• 1

  Draw a right angle triangle inside the circle, with the point of the 90-degree angle touching the outer edge of the circle.

• 2

  Put a mark on the edge of the circle at each point where the lines extending from the 90-degree angle cross the boundary of the circle.

• 3

  Connect the two points marked on the edge of the circle with a straight line.

• 4

  Measure that line. This is the diameter of the circle.

• 5

  Multiply the diameter of the circle by pi (3.14). The result is the circumference, or length around the outside of the circle.

• 6

  Divide the diameter in half to get the radius. Square the radius and multiply it by pi to get the area of the circle.

Right Angle Triangle

• 7

  Find the length of two of the sides of the triangle. In most math problems, you will be given the lengths of two sides when figuring the dimensions of a triangle. If you are not, you can measure two sides and then calculate the third.

• 8

  Decide which version of the Pythagorean theorem you need to apply. If you lack the length of the hypotenuse, use the standard A-squared plus B-squared equals C-squared formula. If you have the hypotenuse and another side, you must square the two sides that you have, and subtract the value of the other side from the squared hypotenuse. The result is the unknown side, squared.

• 9

  Add the length of all three sides of the triangle to find the perimeter, or multiply the base by the height and divide by 2 to get the area.