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Mathematics 9 Online
OpenStudy (anonymous):

need help on the attachment

OpenStudy (turingtest):

what attachment?

OpenStudy (amistre64):

the one that he prolly cant attach quickly enough cause of OS being on a monthly cycle lol

OpenStudy (anonymous):

OpenStudy (anonymous):

haha very funny amistre64

OpenStudy (amistre64):

:) so what do you end up getting for your 1st and 2nd derivatives?

OpenStudy (amistre64):

i see its a product rule and a power rule to play with

OpenStudy (amistre64):

\[x(2-x)^{3/4}\]

OpenStudy (turingtest):

product rule and chain rule on the part in parentheses: \[f'(x)=(2-x)^{3/5}+x(3/5)(2-x)^{-2/5}(-1)\]\[=(2-x)^{-2/5}[(2-x)-3x/5]=(2-x)^{-2/5}(2-8x/5)=0\]

OpenStudy (anonymous):

no its (2-x)^(3/5)

OpenStudy (turingtest):

you can get the critical numbers from this I presume

OpenStudy (amistre64):

\[x'(2-x)^{3/5}+x(2-x)'^{3/5}\] \[(2-x)^{3/5}+x\frac{3}{5}(2-x)^{-2/5}\] \[(2-x)^{3/5}+\frac{3x}{5(2-x)^{2/5}}\] \[5(2-x)^{2/5}(2-x)^{3/5}=5(2-x)\] \[\frac{3x(5(2-x))}{5(2-x)^{2/5}}\] \[\frac{3x(2-x)}{(2-x)^{2/5}}\] \[3x(2-x)^{3/5}=0;x=0,2\] those look almost critical

OpenStudy (amistre64):

i missed it someplcae if wolframs right

OpenStudy (turingtest):

you forgot chain rule on the right and lost a negative sign amistre

OpenStudy (amistre64):

gpt it; i produced instead of sumate

OpenStudy (amistre64):

and the negative too lol

OpenStudy (anonymous):

so is the answer suppose to be -2, also amistre64 I don't get your work on step 4

OpenStudy (amistre64):

step 4 was just so that I could rewrite the numerator with a common denominator

OpenStudy (anonymous):

???

OpenStudy (amistre64):

lets start at step 3

OpenStudy (amistre64):

since i messed it up afterwards anyhoos :)

OpenStudy (anonymous):

ok

OpenStudy (amistre64):

\[(2-x)^{3/5}-\frac{3x}{5(2-x)^{2/5}}\] \[(2-x)^{3/5}*\frac{5(2-x)^{2/5}}{5(2-x)^{2/5}}-\frac{3x}{5(2-x)^{2/5}}\] \[\frac{5(2-x)}{5(2-x)^{2/5}}-\frac{3x}{5(2-x)^{2/5}}\] \[\frac{5(2-x)-3x}{5(2-x)^{2/5}}\] \[\frac{10-5x-3x}{5(2-x)^{2/5}}\] \[\frac{10-8x}{5(2-x)^{2/5}}=0;\ when\ x=\frac{\cancel{10}5}{\cancel{8}4}\]

OpenStudy (amistre64):

and it is undefined at x=2

OpenStudy (amistre64):

so these are important parts to check out

OpenStudy (amistre64):

im guessing it just wants the 1st derivative criticals

OpenStudy (anonymous):

yes I believe so

OpenStudy (amistre64):

so try x=2,5/4 and hopefullt thats it :)

OpenStudy (anonymous):

where did 5/4 come from

OpenStudy (amistre64):

its what the 1st derivative zeros out at

OpenStudy (amistre64):

10-8x = 0 when x=5/4

OpenStudy (anonymous):

oh, you set the numerator equal to zero

OpenStudy (anonymous):

ok so you always set the numerator and denominator equal to zero when solving for the critical points

OpenStudy (amistre64):

yes, criticals are when you zero out the top, and where you have undefineds at, or zeros in the bottom

OpenStudy (amistre64):

they are points of interest

OpenStudy (anonymous):

ok thanks so much

OpenStudy (anonymous):

Also one thing how did you get rid of 3/5 on (2-x)?

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