y=1/корень(3 - х)
f`(x_(o))=[m]lim_{x → x_{o}}\frac{f(x_{o}+ Δx)-f(x_{o})}{x-x_{o}}[/m]
[m]x-x_{o}= Δx[/m]
[m]x=x_{o}+ Δx[/m]
f`(x_(o))=[m]lim_{ Δx →0 }\frac{f(x_{o}+ Δx)-f(x_{o})}{ Δx}[/m]
[m]f(x)=\frac{1}{\sqrt{3-x}}[/m]
f`(x_(o))=[m]lim_{ Δx →0}\frac{\frac{1}{\sqrt{3-(x_{o}+ Δx)}}-\frac{1}{\sqrt{3-x_{o}}}}{ Δx}=lim_{ Δx →0}\frac{\sqrt{3-x_{o}}-\sqrt{3-(x_{o}+ Δx)}}{ Δx\cdot \sqrt{3-(x_{o}+ Δx}\cdot \sqrt{3-x_{o}}}=[/m]
Умножаем числитель и знаменатель на выражение:
[m]\sqrt{3-x_{o}}+\sqrt{3-(x_{o}+ Δx)} [/m]
[m]=lim_{ Δx →0}\frac{(\sqrt{3-x_{o}}-\sqrt{3-(x_{o}+ Δx)})(\sqrt{3-x_{o}}+\sqrt{3-(x_{o}+ Δx)})}{ Δx\cdot \sqrt{3-(x_{o}+ Δx}\cdot \sqrt{3-x_{o}}\cdot (\sqrt{3-x_{o}}+\sqrt{3-(x_{o}+ Δx)})}=lim_{ Δx →0}\frac{3-x_{o}-3+x_{o}- Δx}{ Δx\cdot \sqrt{3-(x_{o}+ Δx}\cdot \sqrt{3-x_{o}}\cdot (\sqrt{3-x_{o}}+\sqrt{3-(x_{o}+ Δx)})}=-\frac{1}{2\sqrt{3-x_{o}}}[/m]