# Very Quick Differentiation Question

#### ozone

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?

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#### SteamKing

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

#### HallsofIvy

Homework Helper
It's very difficult to read what you have written. Are those "2"s after the letters squares? If you cannot use use LaTeX, $c^2= a^2+ b^2- 2ab cos(\theta)$, 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?"

#### ozone

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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