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# A levels maths hopefully a simple easy question watch

1. Could someone tell me why isn't the last part x d2y/dx2 dy/dx ?
Isn't the differential of dy/dx = d2y/dx2?
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2. (Original post by maxintos)

Could someone tell me why isn't the last part x d2y/dx2 dy/dx ?
Isn't the differential of dy/dx = d2y/dx2?
Yes it is. Why do you think you need to multiply it by dy/dx? You're just using the product rule here - if z = vw then z' = v'w + vw'. In this case, put v = x and w = dy/dx and it should become clearer.
3. (Original post by maxintos)

Could someone tell me why isn't the last part x d2y/dx2 dy/dx ?
Isn't the differential of dy/dx = d2y/dx2?
Use the product rule on x.dy/dx and you'll see
4. (Original post by maxintos)

Could someone tell me why isn't the last part x d2y/dx2 dy/dx ?
Isn't the differential of dy/dx = d2y/dx2?
I swear you cant differentiate with that method with respect to 3 variables....
5. (Original post by davros)
Yes it is. Why do you think you need to multiply it by dy/dx? You're just using the product rule here - if z = vw then z' = v'w + vw'. In this case, put v = x and w = dy/dx and it should become clearer.
For some reason I was stuck thinking that you have to use implicit differentiation on dy/dx like you had when differentiating y with respect to x.
6. (Original post by maxintos)
For some reason I was stuck thinking that you have to use implicit differentiation on dy/dx like you had when differentiating y with respect to x.
So are you happy that you understand how they got the result now?
7. (Original post by davros)
So are you happy that you understand how they got the result now?
Yes, with clear head everything makes much more sense.

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