## attack of my horrid math skills, pt. 1

I thought I should start numbering these... anyway, here's another brain-fart where I miss something obvious:

in the book the dude uses:

$$$f(x) = \frac{1}{{30}}\sqrt {a^2 + x^2 } + \frac{1}{{60}}(b - x)$$$

later on he continues, using:

$$$f'(x) = \frac{1}{{30}}\frac{1}{2}(a^2 + x^2 )^{ - 1/2} (2x) - \frac{1}{{60}}$$$

where'd that 2x come from? isn't the derivative of $$$\sqrt {a^2 + x^2 }$$$ just $$$\frac{1}{2}(a^2 + x^2 )^{ - 1/2}$$$?

thanks

 PhysOrg.com science news on PhysOrg.com >> 'Whodunnit' of Irish potato famine solved>> The mammoth's lament: Study shows how cosmic impact sparked devastating climate change>> Curiosity Mars rover drills second rock target
 Well assuming that you mean x instead of b, that 2x comes from the chain rule.
 yea chain rule but also he seems to have confused x for b in the derivative, should be $$\frac{1}{2}(a^2+x^2)^{-1/2}(2x)$$

## attack of my horrid math skills, pt. 1

blah, I'm an idiot . o well, haha thanks.

and yea those two were typos; I fixed them.