Total Differential/Partial Derivative with Fractions from Alpha Chiang Ch. 8

johnjohn

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Dec 28, 2013
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Hello,
So I am looking at this problem on page 209 of Fundamental Mathematical Methods of Economics by Alpha Chiang, Example 3 in section 8.3.

I am finding total differential of (x+y)/(2x2)

For doing the partial with respect to x, I think I am ok. I have:
2x2(1) - (x+y)(4x)
4x4

= (2x2 - 4x2-4xy) / (4x4)

= (-2x2-4xy) / (4x4)

= - (x+2y) / 2x3

The partial with respect to y is 1 / (2x2), but I have no idea how I get that. I am very confused as to how to combine quotient rule with partial derivs (when do I drop the "other" variable, and when not?)

Thanks much.
 
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