Derivatives

Find dy/dx if xy^2 + x^2y + y = 0

Is this correct:

x2y + 2xy +y

Sorry, this is not correct. You'll need to use implicit differentiation. On the first term, for example:

The derivative of xy^2 is x*2y*(dy/dx) + (y^2)*1. Can you handle the rest?
 
wjm11 said:
Find dy/dx if xy^2 + x^2y + y = 0

Is this correct:

x2y + 2xy +y

Sorry, this is not correct. You'll need to use implicit differentiation. On the first term, for example:

The derivative of xy^2 is x*2y*(dy/dx) + (y^2)*1. Can you handle the rest?

I'm not sure I get this, so would it be?

x(2y) + 2(x) y+y =0
x2y + 2xy +y^2 = 0
 
I'm not sure I get this, so would it be?

x(2y) + 2(x) y+y =0
x2y + 2xy +y^2 = 0

Still not correct. You need to read your book.
Example: The derivative of y^2 with respect to x is 2y*(dy/dx).
In your problem you need to differentiate each of the three terms, separate out the terms that have (dy/dx) in them, and finally, solve in terms of dy/dx.
 
wjm11 said:
I'm not sure I get this, so would it be?

x(2y) + 2(x) y+y =0
x2y + 2xy +y^2 = 0

Still not correct. You need to read your book.
Example: The derivative of y^2 with respect to x is 2y*(dy/dx).
In your problem you need to differentiate each of the three terms, separate out the terms that have (dy/dx) in them, and finally, solve in terms of dy/dx.


x2y + 2xy + 0 =
2x + 2xy + 2x + 2xy = 0
4x + 2xy =0
 
What is the derivative of 2xy with respect to x?

We have a product: (2x) * (y)

So we must use the product rule:
Code:
 d            d               d
---- 2xy =  ---- (2x) * y +  ---(y) * 2x
dx           dx               dx

                      dy      
         =  2 * y +  ---- * 2x
                      dx

                     dy
         =  2y + 2x ---
                     dx
If this isn't ringing any bells then you need to consult with your textbook/notes from class on implicit differentiation.
 
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