2(x^2/3) + (x^4/5) +11

i differnetiated this to get

4/3(x^-1/3) + 4/5(x^-1/5)

i know then, that i have to set the differentiated formula = 0. Please help with what i have to do next.

Thanks

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- October 1st 2011, 08:42 AMsalma2011differentiate and find maximum and minimum turning point
2(x^2/3) + (x^4/5) +11

i differnetiated this to get

4/3(x^-1/3) + 4/5(x^-1/5)

i know then, that i have to set the differentiated formula = 0. Please help with what i have to do next.

Thanks - October 1st 2011, 08:46 AMSironRe: differentiate and find maximum and minimum turning point
The first derivative is indeed:

To find the minumum/maximum then you have to solve . What do you get? Afterwards make a sign table to determine where the function increases/decreases. - October 1st 2011, 08:59 AMsalma2011Re: differentiate and find maximum and minimum turning point
I can't remember how to solve it. i know im missing something simple. so can anyone help me solve this please. thank you

- October 1st 2011, 10:08 AMe^(i*pi)Re: differentiate and find maximum and minimum turning point
I suggest finding the lowest common denominators of 3 and 5 and change your exponents into that form:

You can then factor out as a common factor

Can you solve now?

To test whether you have a maximum or minimum check the sign of .

- If you have a maximum
- If you have a minimum
- If you have a point of inflection

- October 1st 2011, 10:13 AMSironRe: differentiate and find maximum and minimum turning point
There're probably different ways to solve the equation, but if you have to solve:

This means there're no solutions, because there's no value wherefore:

or .

So what's your conclusion? - October 1st 2011, 10:59 AMsalma2011Re: differentiate and find maximum and minimum turning point
i solved for x and got x = + or - square root of 3/5

(sorry don't know how to put mathematical functions onto the computer)

and then from the derivative i work out whether it's a maximum or a minimum.

thank you for all your help