in der Mitte hast du \(-2*d *\frac {1} {9} *d= - \frac {2} {9} *d^2= -\frac {2} {9}*(2r)^2\)
alles zusammen: \((2r)^2 -\frac {2} {9} (2r)^2+ \frac {1} {81} (2r)^2 = (2r)^2*( 1-\frac {2} {9} +\frac {1} {81})= (2r)^2( \frac{81-18+1} {81}) \)
Sonstiger Berufsstatus, Punkte: 12.73K
