Posted by **Ifi** on Saturday, October 27, 2012 at 9:56pm.

dx/dy cos x sin y + x^5 = 11

i got dx/dy= (-cos x cos y)/ (-sin x sin y +5x^4)

But the wolfram got

(1- cos x cos y)/(5x^4-sin y sin x), where is the 1 come from?

- Math -
**Reiny**, Saturday, October 27, 2012 at 11:11pm
so we are differentiating

cosx siny + x^5 = 11 implicitly ?

cosx(cosy) dy/dx + siny(-sinx) + 5x^4 = 0

dy/dx = (sinx siny - 5x^3)/(cosx cosy)

which agrees with my Wolfram result

http://www.wolframalpha.com/input/?i=find+dy%2Fdx+for+%28cos%28x%29%29%28sin%28y%29%29+%2B+x%5E5+%3D+11

- Math -
**Reiny**, Saturday, October 27, 2012 at 11:17pm
just noticed you wanted dx/dy (strange)

cosx siny + x^5 = 11

cosx(cosy) + siny(-sinx) dx/dy = 5x^4 dx/dy = 0

dx/dy (5x4 - sinxsiny) = - cosxcosy

dx/dy = -cosxcosy/(5x^4 - sinxsiny)

the same as yours.

- Math -
**Ifi**, Sunday, October 28, 2012 at 4:53am
At reiny .... Thanks

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