c ' (x) = 4x - 3
$$\overline{c}=\frac{2x^2-3x+8}{x}= 2x-3+\frac{8}{x}$$
$$\overline{c} ' = 2-\frac{8}{x^2}$$
$$ε_c(x)=c'(x)*x/c = \frac{4x^2-3x}{2x^2-3x+8}$$
2.    4x-3 = 2x-3 + 8/x
<=>  2x = 8/x
<=>    x = 2    ( x positiv ! )
Also Punkt ( 2 ; 10 ) .
$$ε_c(2)= \frac{10}{10}=1$$
3.  $$\overline{c} ' (x)= 0$$ $$<=>  0= 2-\frac{8}{x^2}$$  $$ <=> 2= \frac{8}{x^2}$$<=>  x^2 = 4  wegen x>0 also  x=2 .
hinreichende Bedingung für Min:
  \( \overline{c} '(x) = 0 \)  und   \( \overline{c} ''(x) >0 \)
erfüllt, wegen \( \overline{c}''(x) = \frac{16}{x^3} \) und \( \frac{16}{8} = 2 \gt 0 \).