0 \Rightarrow \alpha <90" alt="f(x)=x^3-2x^2+3
\\\
f`(x)=3x^2-4x
\\\
f`(a)=f`(-1)=3+4=7
\\\
k=7>0 \Rightarrow \alpha <90" align="absmiddle" class="latex-formula">
0 \Rightarrow \alpha <90" alt="f(x)= \frac{x-1}{x+3}
\\\
f`(x)= \frac{(x-1)`(x+3)-(x-1)(x+3)`}{(x+3)^2} =\frac{x+3-x+1}{(x+3)^2}=\frac{4}{(x+3)^2}
\\\
f`(a)=f`(1)=\frac{4}{(1+3)^2}=0.25
\\\
k=0.25>0 \Rightarrow \alpha <90" align="absmiddle" class="latex-formula">