设四个数为b,bq,bq^2,bq^3,则等差数列为b-1,bq-1,bq^2-4,bq^3-13,则2bq-2=b-1+bq^2-4;2bq^2-8=bq-1+bq^3-13由等差数列性质计算得2bq=b+bq^2-3
①2bq^2=bq+bq^3-6②①*2-②,得2+2q^2-4q=q+q^3-2q^22+4q^2-5q=q^3q^3-4q^2+5q-2=0q^3-q^2-3*q^2+3q+2q-2=0q^2(q-1)-3q(q-1)+2(q-1)=0(q-1)(q^2-3q+2)=0(q-2)(q-1)^2=0q=1或2,代入①,得q=1时无意义,q=2时,b=1,...
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