求和1+3q+5q^2+7q^3+9q^4=

令S=1+3q+5q^2+7q^3+9q^4qS=q+3q^2+5q^3+7q^4+9q^5qS-S=9q^5-2q^4-2q^3-2q^2-2q-1=9q^5-1-2(q^4+q^3+q^2+q)令a=q^4+q^3+q^2+qaq=q^5+q^4+q^3+q^2所以aq-a=q^5-q所以a=(q^5-q)/(q-1)所以qS-S=9q^5-1-2(q^5-q)/(q-1)=(...