Knowing what year a building was constructed will give you a good idea of whether or not aluminum wiring was used instead of another metal. If you do not already know, ask the building's owner or previous owner, landlord, or superintendent. If the building was constructed between 1965 and 1973, it is likely that is has aluminum wiring.  If you can't get the information this way, visit the Library of Congress website at http://www.loc.gov/pictures/collection/hh/ to see if historical records pertaining to  the building are available. Helpful historical documents could include building plans or contracts. Even if the building was built before the rise in popularity of aluminum wiring, don't assume that your wiring is not aluminum. If circuits were added or modified after 1965, installers may have used aluminum wiring for the repairs. Inquire with the building's management company, owner, landlord, or superintendent to see what electrical work was done on the building and when it was done. If you can't find the information you're looking for about the building's history, ask owners or tenant of neighboring buildings what they can tell you about it. Neighbors may remember when the building was constructed. Keep in mind that this may not be the most reliable way to get information, and double check any information you get from your neighbors if you can.
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One-sentence summary -- Find out what year the building was built. Ask about building repairs if the building was constructed before 1965. Speak to neighbors if you can't find the information.


The chain rule is a rule for derivatives that you use when the original function combines a function within another function. The chain rule says that, for two functions f(x){\displaystyle f(x)} and g(x){\displaystyle g(x)}, the derivative of the combination of the two can be found as follows: If y=f(g(x)){\displaystyle y=f(g(x))}, then y′=f′(g)∗g′(x){\displaystyle y^{\prime }=f^{\prime }(g)*g^{\prime }(x)}. Using the chain rule requires that you first define the two functions that make up your combined function. For square root functions, the outer function f(g){\displaystyle f(g)} will be the square root function, and the inner function g(x){\displaystyle g(x)} will be whatever appears under the radical sign. For example, suppose you wish to find the derivative of 3x+2{\displaystyle {\sqrt {3x+2}}}. Define the two parts as follows:  f(g)=g=g12{\displaystyle f(g)={\sqrt {g}}=g^{\frac {1}{2}}} g(x)=(3x+2){\displaystyle g(x)=(3x+2)} To apply the chain rule to the square root of a function, you will first need to find the derivative of the general square root function:   f(g)=g=g12{\displaystyle f(g)={\sqrt {g}}=g^{\frac {1}{2}}}  f′(g)=12g−12{\displaystyle f^{\prime }(g)={\frac {1}{2}}g^{-{\frac {1}{2}}}} f′(g)=12g{\displaystyle f^{\prime }(g)={\frac {1}{2{\sqrt {g}}}}}   Then find the derivative of the second function:  g(x)=(3x+2){\displaystyle g(x)=(3x+2)} g′(x)=3{\displaystyle g^{\prime }(x)=3} Recall the chain rule, y′=f′(g)∗g′(x){\displaystyle y^{\prime }=f^{\prime }(g)*g^{\prime }(x)}, and then combine the derivatives as follows:  y′=12g∗3{\displaystyle y^{\prime }={\frac {1}{2{\sqrt {g}}}}*3} y′=12(3x+2∗3{\displaystyle y^{\prime }={\frac {1}{2{\sqrt {(3x+2}}}}*3} y′=32(3x+2{\displaystyle y^{\prime }={\frac {3}{2{\sqrt {(3x+2}}}}}
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One-sentence summary -- Review the chain rule for functions. Define the functions for the chain rule. Find the derivatives of the two functions. Combine the functions in the chain rule.


You can begin with a milder method, or start with this one if you don’t want to take your chances on leaving the stain for too long. It’s also an option to use a clear alcohol, like vodka, if you don’t have isopropyl alcohol around. Just try not to drink any of it while you clean. Nail polish remover and hydrogen peroxide will work similarly to isopropyl alcohol. Don’t start working on the stain just yet. Instead, find a hidden or small spot on the wood floor. Dab the cloth on a very small spot to make sure it doesn’t damage the wood. If it does, abandon this method now. It’s okay. There’s another way to remove the stain. It is still an option to use the alcohol even if it does slightly discolor the wood. You could just sand it down and go over the floor with a wood stain to make it like new again. Use the cloth that has been dampened with isopropyl alcohol to begin scrubbing off the stain. You’ll know the alcohol is working if the stain begins to transfer to the cloth. Continue to scrub until the stain is gone and relief begins to wash over you. Once the stain has been scrubbed off, rinse off the wood. You can pour some water on the wood and dry it off with a towel. Or, wet a fresh cloth and then let the wood air dry. You’re done! Sit back and relax.
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One-sentence summary --
Pour isopropyl alcohol on a cloth. Test the surface of the wood. Wipe off the stain with a cloth and isopropyl alcohol. Rinse and dry the wood.