Draw a line from the center of the circle to anywhere on the circle's edge. This line is the "radius" of the circle, often written as just r in math equations and formulas.  Note: if your math problem doesn't tell you the length of the radius, you might be looking at the wrong section. Check whether the sections for Diameter or Area make more sense for your problem. Extend the line you just drew so it reaches the circle edge on the other side. You've just drawn a second radius. The two radii stuck together have a length of "2 x the radius," written as 2r. The length of this line is the "diameter" of the circle, often written d. The π symbol, also written as pi. It isn't a magical number that just happens to work in this kind of math problem. Actually, the number π was originally "discovered" by measuring circles: if you measure the circumference of any circle (for instance with a tape measure), and then divide by the diameter, you'll always end up with the same number. This number is unusual because it can't be written out as a simple fraction or decimal. Instead, we can round to a "close enough" number like 3.14. Even the π button on a calculator doesn't use the exact value of π, although it is close enough. As explained above, π just means "the number you get when you divide the circumference by the diameter." In the form of a math formula: π = C / d. Since we know the diameter equals 2 x the radius, we can also write this as π = C / 2r. C is just a shorter way of writing "circumference." We want to find out what the circumference is, which is C in this math problem. If you multiply both sides by 2r you get π x 2r = (C / 2r) x 2r, which is the same as 2πr = C  You might have written the left side as π2r, which is also correct. People like to move the numbers in front of the symbols just so the equation is easier to read, and this doesn't change the result of the equation. In a math equation, you can always multiple the left side and the right side by the same amount and still end up with a correct equation. Now we know that 2πr = C. Look back at the original math problem to see what r (the radius) equals. Then replace π with 3.14, or use a calculator's π button to get a more accurate answer. Multiply 2πr together using these numbers. The answer you get is the circumference.  For example, if the radius is 2 units long, then 2πr = 2 x (3.14) x (2 units) = 12.56 units = the circumference. In the same example, but using a calculator's π button for better accuracy, you'll get 2 x π x 2 units = 12.56637... units but unless instructed otherwise by your teacher, you can round the number to 12.57 units.
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One-sentence summary -- Draw a "radius" on the circle. Draw a "diameter" across the circle. Understand π ("pi"). Write down the definition of π as an algebra problem. Change this problem so you are solving for C, circumference. Plug in the numbers to solve for C.


Mitral stenosis often presents with a heart murmur that can be heard when your doctor listens with his or her stethoscope. Although this is not enough to diagnose mitral stenosis, it is suspicious of a heart problem and would be an indication for your doctor to order further investigative tests. A chest x-ray is normally one of the first tests your doctor will order, if he or she suspects a lung and/or a heart problem, such as mitral stenosis. A chest x-ray allows your doctor to examine your lungs for fluid build-up (called "pulmonary edema") which may go hand-in-hand with mitral stenosis. Your doctor can also evaluate for enlargement of any of the chambers of your heart, such as the right atrium, which may also be a sign of mitral stenosis.  A chest x-ray is also useful in ruling in or ruling out other heart or lung conditions that may present similarly to mitral stenosis. It is for this reason that it is normally one of the first investigative tests that is ordered. In the evaluation of heart or lung problems such as mitral stenosis, an ECG (sometimes accompanied by an exercise stress test) can be helpful. An ECG is able to detect the amount of "stress" on the heart in various situations. In order to confirm the diagnosis of mitral stenosis (or of any other form of valvular heart disease), an echocardiogram is needed. The first type performed will normally be a TTE (transthoracic echocardiogram). In a TTE, the ultrasound probe is placed on the outside of your chest. It then projects a real-time, colored, moving image of the heart on a screen, where the doctor can look at the structure of your heart as well as the flow of blood with each heartbeat.  The color in the TTE can help indicate the flow of blood. A TTE may be sufficient to observe and confirm the diagnosis of mitral stenosis. If it is not, a TEE (transesophageal echocardiogram) may be ordered. In a TEE, rather than the ultrasound probe being placed on the outside of your chest, it is inserted into your esophagus. Your esophagus is much closer to your heart anatomically, so a TEE can provide a much more detailed view than a TTE, which can aid in the diagnosis of mitral stenosis.
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One-sentence summary --
Have your doctor listen for a heart murmur with a stethoscope. Get a chest x-ray. Consider an ECG (electrocardiogram). Receive an echocardiogram to definitively diagnose mitral stenosis.