\(K(v) = 0,002v^2-0,18v+8,55\) für \(v>40 km/h\)
\(K´(v) = 0,004v-0,18\)
A) \( 0,004v-0,18=0\) \(v=45 \frac{km}{h}\)
B) \(7 = 0,002v^2-0,18v+8,55\)
\( 0,002v^2-0,18v=-1,55|*500\)
\( v^2-90v=-775\)
\( (v-45)^2=-775+(\frac{90}{2})^2=1250 |\sqrt{~~}\)
\( (v-45)=-775+(\frac{90}{2})^2=1250 |\sqrt{~~}\)
\( (v-45)≈35,36 \)
\( v≈80,36\frac{km}{h}\ \)