RULES RELATIVE TO THE CIRCLE.
The circle contains a greater area than any other plane figure bounded by an equal perimeter or outline.
TO FIND CIRCUMFERENCE—
| Multiply diameter by | 3.1416. |
| Or divide diameter by | 0.3183. |
TO FIND DIAMETER—
| Multiply circumference by | 0.3183. |
| Or divide circumference by | 3.1416. |
TO FIND RADIUS—
| Multiply circumference by | 0.15915. |
| Or divide circumference by | 6.28318. |
TO FIND SIDE OF AN INSCRIBED SQUARE—
| Multiply diameter by | 0.7071. |
| Or multiply circumference by | 0.2251. |
| Or divide circumference by | 4.4428. |
TO FIND SIDE OF AN EQUAL SQUARE—
| Multiply diameter by | 0.8862. |
| Or divide diameter by | 1.1284. |
| Or multiply circumference by | 0.2821. |
| Or divide circumference by | 3.545. |
SQUARE—
| A side multiplied by | 1.4142 equals diameter of its circumscribing circle. | ||
| A side multiplied by | 4.443 equals circumference of its circumscribing circle. | ||
| A side multiplied by | 1.128 equals diameter | } | of an equal circle. |
| A side multiplied by | 3.545 equals circumference | ||
| A side multiplied by | 1.273 equals circle inches | ||
TO FIND THE AREA OF A CIRCLE—
| Multiply circumference by one-quarter of the diameter. | |
| Or multiply the square of diameter by | 0.7854. |
| Or multiply the square of circumference by | .07958. |
| Or multiply the square of 1⁄2 diameter by | 3.1416. |
Contents of cylinder = area of end × length. Contents of wedge = area of base × 1⁄2 altitude. Surface of cylinder = area of both ends × length × circumference. Surface of sphere = diameter squared × 3.1416, or = diameter × circumference. Contents of sphere = diameter cubed × .5236. Contents of pyramid or cone, right or oblique, regular or irregular = area of base × 1⁄3 altitude. Area of triangle = base × 1⁄2 altitude. Area of parallelogram = base × altitude. Area of trapezoid = altitude × 1⁄2 the sum of parallel sides.