⚠ (\partial)/(\partial x)(r) is read as dif(r,x): use dif(expression, variable) for a derivative with respect to that variable, use (numerator)/(denominator) for a quotient

Differentiate with respect to x while holding r constant

Let's perform the differentiation: $\frac{\mathrm{d}}{\mathrm{d}x}\left(r\right)$

▶Derivative:   $0$