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Angry at Math

Posted: Fri Jan 22, 2016 5:48 pm
by Natalya
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.

Re: Angry at Math

Posted: Fri Jan 22, 2016 6:22 pm
by Keldoclock
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 :)

Re: Angry at Math

Posted: Fri Jan 22, 2016 6:40 pm
by mgb519
What he meant to say was

f(x)=ln(x+3)
f'(x)=1/(x+3)

Re: Angry at Math

Posted: Fri Jan 22, 2016 6:46 pm
by mgb519
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.

Re: Angry at Math

Posted: Fri Jan 22, 2016 7:47 pm
by Natalya
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.

Re: Angry at Math

Posted: Fri Jan 22, 2016 11:27 pm
by Ham
only autists really need calc in the real world

Re: Angry at Math

Posted: Mon Feb 15, 2016 8:38 pm
by Natalya
Image

Am I doing this wrong?

Re: Angry at Math

Posted: Mon Feb 15, 2016 11:00 pm
by collsipp
When distributing the power, does it affect the coefficient as well?
Image
Other than that, it appears to be OK.

Re: Angry at Math

Posted: Mon Feb 15, 2016 11:26 pm
by Natalya
Oh shit so like does that mean the right part is (2^½)(x^½) ?

Re: Angry at Math

Posted: Tue Feb 16, 2016 8:24 am
by Falk
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)

Re: Angry at Math

Posted: Tue Feb 16, 2016 10:51 am
by vebulus
...Everything said in this post is so high above my clearance level I need to report to a termination booth.

Re: Angry at Math

Posted: Tue Feb 16, 2016 10:56 am
by Kommander Ken
Makes me glad I'm an art student.

Re: Angry at Math

Posted: Tue Feb 16, 2016 11:02 am
by Overwatch_Elite
fucking nerds

Re: Angry at Math

Posted: Tue Feb 16, 2016 11:58 am
by Brikguy0410
colette, get in this thread now

Re: Angry at Math

Posted: Tue Feb 16, 2016 1:08 pm
by mgb519
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.