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December 19, 2014

December 19, 2014

Posted by **Ifi** on Saturday, October 27, 2012 at 10:25am.

y= (9+((x-9)/6)^1/5)^1/2 ?

Hope u can give me the way how to calculate it. ^^

I got 1/60 ((x-9)/6) ^ (-9/10), i think my answer is wrong because i check at wolfram website the ans is differrent from mine (sorry i didnt write the ans bcus the ans is quite long and difficult to type)

- Math -
**Reiny**, Saturday, October 27, 2012 at 1:01pmnot quite ....

let u = ( (x-9)/6 )^(1/5)

then y = (9 + u)^1/2

dy/du = (1/2)(9+u)^(-1/2)

du/dx = (1/5)( (x-9)/6 )^(-4/5) (1/6)

= (1/30) ( (x-9)/6 )^(-4/5)

so dy/dx = dy/du * du/dx

= (1/2)(9 + u)^-1/2) (1/30) ( (x-9)/6 )^(-4/5)

= (1/60) (9 + ( (x-9)/6 )^(1/5)^(-1/2) ( (x-9)/6 )^(-4/5)

I suggest you check my steps for any errors, I should have written it out on paper first.

Wolfram seems to have performed some kind of complicated simplification.

How about this way:

square both sides:

y^2 = 9 + ( (x-9)/6 )^1/2 , then by implicit differentiation,

2y dy/dx = (1/2)( (x-9)/6) )^(-1/2)

dy/dx = (1/4)(√(6/(x-9) ) / y

or √6/(4y√(x-9) ) , that's not bad

- Math - hmm -
**Steve**, Saturday, October 27, 2012 at 2:45pmnot bad, but

y^2 = 9 + ((x-9)/6)^(1/5)

2y dy/dx = 1/5 ((x-9)/6)^(-4/5)

dy/dx = 1/(10y ((x-9)/6)^(4/5))

- Got me - Math -
**Reiny**, Saturday, October 27, 2012 at 2:50pmthanks for looking after me,

rotten copy errors.

- Math -
**Ifi**, Saturday, October 27, 2012 at 9:04pmthanks for the calculation but i think there is a mistake at implicit diff.

y^2= 9 + ((x-9)/6)^(1/5)

2y dy/dx = 1/5 ((x-9)/6)^(-4/5)) (1/6)

dy/dx = 1/60y ((x-9)/6)^(-4/5) ..... Sorryif im wrong

Btw why at wolfram the answer is

1/( 60y(-9+y^2)^4). Why is the x become y^2 and why there are no 6 and ^(4/5)?

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