Answer
2
Work Step by Step
The slope of the tangent line through the point on the graph of $f$ where $x=a$
is given by the instantaneous rate of change, or derivative
$m_{tan}=$ slope of tangent $=$ instantaneous rate of change$=$derivative
$=f^{\prime}(a)=\displaystyle \lim_{h\rightarrow 0}\frac{f(a+h)-f(a)}{h} ,$
assuming the limit exists.
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Let P be $(a,f(a))$, since it is on the graph of f.
From the graph, we read (estimate) two points from the tangent line at P:
(0,0) and (2,4)
The slope of the tangent line:
$m=\displaystyle \frac{y_{2}-y_{1}}{x_{2}-x_{1}}=\frac{4-0}{2-0}=\frac{4}{2}=2,$
so, we estimate
$f^{\prime}(a)=m=2$
