Answer
a) $-1$
b) $ y=-x+5$
Work Step by Step
a) Now, $ m_{\tan}=\lim_\limits{ h\to 0} \dfrac{f(0+h)-f(0)}{h}$
or, $=\lim_\limits{ h\to 0} \dfrac{2h^2-h+5-5}{h}$
or, $=\lim_\limits{ h\to 0} \dfrac{2h^2-h}{h}$
At $(0,5)$; $ m_{\tan}=-1$
b) The equation of a line is: $ y=mx+c $
Now, $ y-5=-1(x-0) \implies y=-x+5$
