dY=-b2/(1-c1-b1)*1/k2*(-dM/P+k1dY)      | hintere Klammer ausmultiplizieren
dY=-b2/(1-c1-b1)*1/k2*(-dM/P) -b2/(1-c1-b1)*1/k2*(k1dY)    | + b2/(1-c1-b1)*1/k2*(k1dY)  
dY +b2/(1-c1-b1)*1/k2*(k1dY)  = -b2/(1-c1-b1)*1/k2*(-dM/P)        | links dy ausklammern
dY (1  +   b2/(1-c1-b1)*1/k2*k1)  = -b2/(1-c1-b1)*1/k2*(-dM/P)