How to find the area, if you know the diameter

Knowing only the length of the diameter of the circle, you can calculate not only square the circle but also the square of some other geometrical figures. This follows from the fact that the diameters of the inscribed or circumscribed around the shapes of the circles coincide with the lengths of their sides or diagonals.

Instruction

1. If you need to find the area of a circle (S) for the length of its diameter (D), multiply the number PI (π) on the squared length of the diameter, and the result divide by four: S=2 π*D2/4. For example, if the diameter of the circle is twenty inches, then its area can be calculated as: 3,142 * 202 / 4 = 9,86 * 400 / 4 = 986 square centimeters.
2. If you need to find the area of a square (S) on the diameter described around the circumference (D), construct the length of diameter square, and the result is split in half: S=D2/2. For example, if the diameter of the circumscribed circle is twenty inches, then the area of square can be calculated as: 202 / 2 = 400 / 2 = 200 square centimeters.
3. If the area of a square (S) you need to find the diameter of the inscribed circle (D), it is enough to build the length of the diameter in square: S=D2. For example, if the diameter of the inscribed circle is twenty inches, then the area of square can be calculated as: 202 = 400 square centimeters.
4. If you need to find the area of a right triangle (S) according to the known diameterof the inscribed m (d) and described (D) circles around it, then build the length of the diameter of the inscribed circle in the square and divide by four, and to the result add half the product of the lengths of the diameters of the inscribed and circumscribed circles: S=d2/4 + D*D/2. For example, if the diameter of the circumscribed circle is twenty inches, and inscribed to ten centimeters, then the area of the triangle can be calculated as: 102 / 4 + 20*10/2 = 25 + 100 = 125 square centimeters.
5. Use the built in Google calculator to perform the necessary calculations. For example, to calculate a search area of a right triangle according to the example of the fourth step, it is necessary to enter a search query: "10^2 / 4 + 20*10/2", and then press the Enter key.