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# help: differential of an exponential watch

1. ive been given the following function to differentiate and find the turning points.

z = e^(2x^2-12x-12xy+y^2-4y)

i do partial differentiation but that only leads to 8x = 7y+ 4 and therefore cant find the stationary point.

any help much appreciated
2. Show your working? It comes out fine for me.
3. (Original post by Mr M)
Show your working? It comes out fine for me.
Zx = (4x-12-12y)e^(2x^2-12x-12xy+y^2-4y)

Zy = (-12x+2y-4)e^(2x^2-12x-12xy+y^2-4y)

then i set them equal to each other to find the turning points but get stuck there
4. (Original post by ilikemaths1)
Zx = (4x-12-12y)e^(2x^2-12x-12xy+y^2-4y)

Zy = (-12x+2y-4)e^(2x^2-12x-12xy+y^2-4y)

then i set them equal to each other to find the turning points but get stuck there
Set them equal to zero not each other?
5. This document will help with this topic.

http://personal.maths.surrey.ac.uk/s...x_min_2var.pdf

6. (Original post by Mr M)
This document will help with this topic.

http://personal.maths.surrey.ac.uk/s...x_min_2var.pdf
i find the article really helpful, thank you very much
7. (Original post by Mr M)
This document will help with this topic.

http://personal.maths.surrey.ac.uk/s...x_min_2var.pdf
do you get y = -40/34?
8. (Original post by ilikemaths1)
do you get y = -40/34?
That cancels down but yes.
9. (Original post by Mr M)
This document will help with this topic.

http://personal.maths.surrey.ac.uk/s...x_min_2var.pdf
Sorry to hijack this thread but do you know any good ways of remembering how to classify stationary points? It seems simple but I can never remember the different conditions for the different types of points.
10. (Original post by james22)
Sorry to hijack this thread but do you know any good ways of remembering how to classify stationary points? It seems simple but I can never remember the different conditions for the different types of points.
I just learned them by covering them up and writing them down and then checking I had it right. I can still remember them 25 years later so it must have worked.

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