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

Differentiate with respect to z while holding y constant

Let's differentiate: $\frac{\mathrm{d}}{\mathrm{d}z}(y+z)$

$\frac{\mathrm{d}}{\mathrm{d}z}\left(y\right)+1$

$0+1$

▶Derivative:   $1$