Angry at Math

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Natalya
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Angry at Math

Post by Natalya » Fri Jan 22, 2016 5:48 pm

Fucking logarithm derivatives.

I know all the log rules. Power, Quotient, Product...

But what they never show you is what to do with shit inside brackets.

ln(x²) ... that's easy you can simplify to 2ln(x) which is just 2/x

But ln(x+3) what the fuck? Why don't they show us rules that cover simple shit like this? So angry. :fist:

I know ln(3) is like a bullshit number and the derivative is 0. I know ln(x)'s derivative is 1/x. But like addition of a variable and some other crap inside the brackets why isn't that a rule they teach us?

I go on Google and I get Yahoo Answers but they're always writing shit like dx/du dy blah blah... why can't they just explain the rule to me in english? I am sure it is VERY simple.

"When you see addition inside the log you just do this." You know, easy to understand words. Not 70 symbols they don't use in class.
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Re: Angry at Math

Post by Keldoclock » Fri Jan 22, 2016 6:22 pm

You aren't angry at math. You are angry at yourself for not paying attention to high school algebra, or forgetting it.

The simplest form of ln(x+3) is ln(x+3). Log rules only allow you to simplify multiplication and division. If you are doing classwork and see ln(x+3) it's probably part of adding or mulitiplying logs together. If it's outside of that context, then what you should do with ln(x+3) is context-dependent :)
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Re: Angry at Math

Post by mgb519 » Fri Jan 22, 2016 6:40 pm

What he meant to say was

f(x)=ln(x+3)
f'(x)=1/(x+3)
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Re: Angry at Math

Post by mgb519 » Fri Jan 22, 2016 6:46 pm

Basically, for problems like this, you have to use the chain rule. See, when you have ln(x+3), you treat the inside like a single variable. It can be rewritten as ln(u) to illustrate this, where u in turn is x+3. When you do that, however, you have to multiply by the derivative of the inside. So you have 1/u=1/(x+3), and then you multiply by the derivative of (x+3). Which it turns out is 1, so it doesn't change anything.
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Re: Angry at Math

Post by Natalya » Fri Jan 22, 2016 7:47 pm

mgb519 wrote:What he meant to say was

f(x)=ln(x+3)
f'(x)=1/(x+3)
See I knew it was fucking simple.
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Re: Angry at Math

Post by Ham » Fri Jan 22, 2016 11:27 pm

only autists really need calc in the real world
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Re: Angry at Math

Post by Natalya » Mon Feb 15, 2016 8:38 pm

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Am I doing this wrong?
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Re: Angry at Math

Post by collsipp » Mon Feb 15, 2016 11:00 pm

When distributing the power, does it affect the coefficient as well?
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Other than that, it appears to be OK.
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Re: Angry at Math

Post by Natalya » Mon Feb 15, 2016 11:26 pm

Oh shit so like does that mean the right part is (2^½)(x^½) ?
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Re: Angry at Math

Post by Falk » Tue Feb 16, 2016 8:24 am

I don't yhink you're allowed to split the root like that since it has a minus between the terms. If there were a * or / inbetween the 4 and 2x then you would be allowed to, but all you can do here to simplify is factor 2, so it's (2)^-0.5 * (2-x)^-0.5

What I do to test if I'm allowed to do an operation is to do it on my calculator without variables. Eg. Do sqrt(4-2) and sqrt(4)-sqrt(2) and see if they are the same (in this case they aren't)
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Re: Angry at Math

Post by vebulus » Tue Feb 16, 2016 10:51 am

...Everything said in this post is so high above my clearance level I need to report to a termination booth.

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Re: Angry at Math

Post by Kommander Ken » Tue Feb 16, 2016 10:56 am

Makes me glad I'm an art student.

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Re: Angry at Math

Post by Overwatch_Elite » Tue Feb 16, 2016 11:02 am

fucking nerds

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Re: Angry at Math

Post by Brikguy0410 » Tue Feb 16, 2016 11:58 am

colette, get in this thread now

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Re: Angry at Math

Post by mgb519 » Tue Feb 16, 2016 1:08 pm

why are you trying to do things to it? Because I can't picture why you would want to break that up, let alone why it should be possible.
Tzan wrote:
Semaj Nagirrac wrote:Well, I took some land without checking if it was owned by a faction or not. I'm not going to be banned, am I? I can destroy everything if need be.
That's what Hitler said,
in 1938.

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