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Very Quick Differentiation Question

  • Thread starter ozone
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122
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First I attempted to ipmlicitly differentiate
c2 = a2 + b2 -2abcos(theta)

da/db


I almost got the correct solution according to MIT's key, however I missed one part. The cos from the original function remained cos, and I had differentiated it to -sin.

I'm just wondering why it remained cos instead of being differentiated?
 

SteamKing

Staff Emeritus
Science Advisor
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Unless theta is a function of b, then cos(theta) is a constant when trying to find the derivative with respect to b.
 

HallsofIvy

Science Advisor
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It's very difficult to read what you have written. Are those "2"s after the letters squares? If you cannot use use LaTeX, [itex]c^2= a^2+ b^2- 2ab cos(\theta)[/itex], at least use "^" to indicate powers: c^2= a^2+ b^2- 2ab cos(theta).

But the real question is "differentiate what variable with respect to what other variable?"
 
122
0
Thanks, but SteamKing already helped solve my problem.. Sorry I will be sure to start using the forums code based mathematical notation from now on.
 

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