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 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 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 button on a calculator doesn't use the exact value of , although it is close enough. As explained above, just means "the number you get when you divide the circumference by the diameter." In the form of a math formula: = C / d. Since we know the diameter equals 2 x the radius, we can also write this as = 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 x 2r = (C / 2r) x 2r, which is the same as 2r = C You might have written the left side as 2r, 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 2r = C. Look back at the original math problem to see what r (the radius) equals. Then replace with 3.14, or use a calculator's button to get a more accurate answer. Multiply 2r together using these numbers. The answer you get is the circumference. For example, if the radius is 2 units long, then 2r = 2 x (3.14) x (2 units) = 12.56 units = the circumference. In the same example, but using a calculator's button for better accuracy, you'll get 2 x 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 ("pi"). Write down the definition of as an algebra problem. Change this problem so you are solving for C, circumference. Plug in the numbers to solve for C.

Q: This step is only necessary when you'll be handling extremely concentrated acid solutions, such as 18M sulfuric acid, or 12M hydrochloric acid. Cool the water you'll be using by keeping it in a container surrounded by ice for at least 20 minutes before the dilution begins. For most dilutions, the water can be at room temperature. For projects involving careful measurement, such as titration, use a volumetric flask. For most practical purposes, an Erlenmeyer flask can be used instead. In either case, choose a container that can easily contain your total desired volume, with plenty of space remaining, to minimize splashes over the rim. You don't need to carefully measure this water, as long as it came from a container that was carefully measured to contain the total required amount of water. If using a small volume of acid, use a graduated (Mohr) pipette or volumetric pipette with a rubber bulb on top. For larger volumes, place a funnel in the neck of the flask, and slowly pour in a small quantity of the acid using a graduated cylinder. Never use a mouth pipette in a chemistry lab. Strong acids may generate lots of heat when added to water. If the acid was highly concentrated, the solution may splatter or produce corrosive fumes. If this happens, you will need to perform the entire dilution in very small doses, or cool the water in an ice bath before you continue. Allow the solution time to cool off between each dose, especially if you notice heat, fumes, or spatter. Continue until the required amount of acid has been added. This amount was calculated as V1 above. For best results, you can stir the solution with a glass stirring rod after each addition of acid. If the size of the flask makes this impractical, stir the solution after the dilution is complete and the funnel is removed. Pour the acid solution you created into a clearly labeled container, preferably a PVC coated glass bottle, and store in a safe location. Rinse the flask, funnel, stirring rod, pipette, and/or graduated cylinder in water to remove all traces of acid.
A: Cool water in an ice bath when using concentrated acids. Add distilled water to a large flask. Add a tiny quantity of acid. Allow the solution to cool off. Add the remaining acid in small doses. Stir the solution. Store the acid and rinse the tools.

Article: Do you wash your hair every day? This can dry it out, since you're washing away natural protective oils that help your hair stay strong and healthy. Washing them out causes your hair to be susceptible to breakage and split ends, which means you'll need more maintenance trims and it'll take much longer to grow your hair to the length you desire. To keep your hair healthy, follow this routine: Wash your hair about three or four times a week. At first your hair might seem oily, but soon your scalp will produce just enough oil to moisturize your hair without overdoing it. Wash your hair with the coldest water you can handle. Washing with hot water leads to split ends and frizz, while cold water keeps the hair shaft smooth and healthy. The way you dry your hair can also have a big impact on how quickly it grows out. Do you tend to roughly towel dry your hair, brush out the tangles, then blow it dry? This sets your hair up for major breakage. When you're growing it out, ditch that routine and try this: When you get out of the shower, gently squeeze the excess water from your hair, then pat it dry with a soft towel. Don't rub or massage it; just pat it. Comb your hair with a wide-toothed comb, which is easier on hair than a brush. Work through tangles gently, so you don't break the hair as you pull through. Let your hair air dry most days. It's the healthiest way to dry your hair. Some days letting your hair air dry just won't do - especially if you're going to a special event and you want it to look well styled. On the days when you want your hair to look sleek and styled, try these alternatives: Blow your hair using the cold setting. This is a lot less harsh on your hair, but it can still make your hair look smoother than air drying. Curl your hair without heat. Use the t-shirt method, the sock bun method, or another cool-curling method to curl your hair instead of using a curling iron or hot rollers.
Question: What is a summary of what this article is about?
Change the way you wash your hair. Dry your hair with care. Style your hair gently.