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Math Mnemonic 1 - September 20, 2010
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Spiked Math Comic - Math Mnemonic 1



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20 Comments

Didn't get it :((

The line on the bottom explains the mnemonic.

Remembering these signs is, of course, a universal problem. I tell my students to look at the graphs (in the interval [0,pi/2]). Sine goes up, so its derivative is positive. Cosine goes down, so its derivative is negative. Revert these to get the rules for integrals. Dunno. May be I should attempt to translate this, but...

I hate tan...
In fact, doing claculus stuff with any trig functions but sin and cos is just such a hassle.

That's the only way I can remember it - until now. Although I don't know what "IS DC NEGATIVE" is supposed to mean other than the abbreviation.

Same here. I don't know what "IS DC NEGATIVE" means.

aww Mike you pushed the constant to the corner..., ignored the Tan. mean you... wait till next summer for tan ;)

The way I remember is trig functions that start with a "c" (eg: cos, cot, csc) are negative when you differentiate and the ones that don't start with "c" are negative when you integrate (with the exception of csc^2).

Maybe DC here refers to 'Direct Current' which, unlike AC (Alternating Current), does not change its direction ('sign').

No! The line below explains the mnemonic! It is about calculus!

I don't really like Math mnemonics which are just mnemonics. I don't like this one.
I believe that "differentiate: the cycle sin -> cos -> -sin > -cos -> sin; integrate: invert the cycle" is much better.

tan(x) for the IS DC negative rule... I'll remember it every time now. I won't remember what it means, but I'll remember "IS DC negative"

Isn't it kind of redundant? I mean, integrating sine and differentiating cosine are essentially the same thing, just in different directions, so if one gives a negative then so will the other. You could just say 'IS negative'. Unless there's a meaning I'm not aware of that makes 'IS DC negative' easier to remember.

Maybe he just doesn't like USA's capitol.

...or perhaps the capital, since the capitol is the building.

Or maybe he means direct current ;) that is pretty negative.

All you need to do is remember that dsin(x)/dx = cos(x), and then remember that swapping sine and cosine introduces a negative, as does switching from derivatives to integrals.

true, but "is dc negative" is even easier to remember

It is easier if you swap is and DC. "DC is negative" and make an association with DC (direct) current. When I am integrating i just think a battery (DC source) and this mnemonic comes to my mind.

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