To find the derivative of $f(x)=x^2-3x+21$ at $x=4$, would you just find the derivative of $f(x)$, which is $2x-3$, and plug in 4 for $x$, to get 5?
To find the derivative of $f(x)=x^2-3x+21$ at $x=4$, would you just find the derivative of $f(x)$, which is $2x-3$, and plug in 4 for $x$, to get 5?
yes ... $f'(4) = 5$