Derivative of $$$k + r$$$ with respect to $$$r$$$
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Your Input
Find $$$\frac{d}{dr} \left(k + r\right)$$$.
Solution
The derivative of a sum/difference is the sum/difference of derivatives:
$${\color{red}\left(\frac{d}{dr} \left(k + r\right)\right)} = {\color{red}\left(\frac{dk}{dr} + \frac{d}{dr} \left(r\right)\right)}$$Apply the power rule $$$\frac{d}{dr} \left(r^{n}\right) = n r^{n - 1}$$$ with $$$n = 1$$$, in other words, $$$\frac{d}{dr} \left(r\right) = 1$$$:
$${\color{red}\left(\frac{d}{dr} \left(r\right)\right)} + \frac{dk}{dr} = {\color{red}\left(1\right)} + \frac{dk}{dr}$$The derivative of a constant is $$$0$$$:
$${\color{red}\left(\frac{dk}{dr}\right)} + 1 = {\color{red}\left(0\right)} + 1$$Thus, $$$\frac{d}{dr} \left(k + r\right) = 1$$$.
Answer
$$$\frac{d}{dr} \left(k + r\right) = 1$$$A