The formula for area of a circle is r^2*pi=a. If you know that the radius is three, then you can find the area of at 9*pi, or 9*3.141592653589793238462643383279502884197169399375105820974944592307816406286208... This can be simplified to about 27. The formula for circumference is diameter times pi. The diameter is the same as two radii, so the formula can also be two times radius times pi. If the radius is three, then the diameter is six. Six times pi can simplify to about 18.
Pi is an interesting number. For one thing, it is an irrational number, which means that it goes on forever and never repeats. Pi can be used for a number of things, although most have to do with circles. For example, if you multiply pi by the radius squared of a circle, you get the area. Pi is usually not written out like it is in the title. It is simplified to the pi symbol or 3.14,. An example of the area of a circle formula could be the following. if the radius of a circle is 2, then square it (4), and multiply it by the pi substitute of you choice: Either 4 (pi symbol) or 4*3.14=12.56. The formula can also be done in reverse. The square root of the area of a circle divided by pi is the radius.

Another thing that can be found with pi is the circumference, or the length around a circle. That can be found by the diameter times the value of pi, or diameter times two times radius. For example, if the radius is two, then the diameter is 4, and the circumference is  Either 4 (pi symbol) or 4*3.14=12.56.
Once you know the equation of a line, and that equation is in y=mx+b form, there are certain steps to graphing that line. First, take a Cartesian coordinate plane and place a dot on the value of the b. Then, put the slope into a fraction, if it isn't already, and move vertically the value of the numerator, and horizontally, the number of the denominator. After that, put a dot where you end up. Then use a ruler or straight-edge to draw a straight line connecting the two dots and continuing to the ends of the plane.

For example, if your equation is y=3x+1, put a dot at 0,1 or 1 on the y axis. Then put 3 into a fraction: 3/1. Move up 3 and over 1, then put another dot. Take a ruler, and connect those two points. If your equation is y=-3-1, put a dot at 0,-1 then move down three and over 1.