已知a3=1.5, S3=3 求q和a1的直
我需要解题过程
参考答案:q=(1±√5)/2
a1=3/(3±√5)
a3=a1q^2=1.5......(1)
s3=a1+a1q+a3=a1+a1q+1.5=3
a1*(1+q)=1.5......(2)
a1q^2=a1*(1+q)
q^2-q-1=0
q=(1±√5)/2
a1=1.5/(1+q)=1.5/[1+(1±√5)/2]=3/(3±√5)
我需要解题过程
参考答案:q=(1±√5)/2
a1=3/(3±√5)
a3=a1q^2=1.5......(1)
s3=a1+a1q+a3=a1+a1q+1.5=3
a1*(1+q)=1.5......(2)
a1q^2=a1*(1+q)
q^2-q-1=0
q=(1±√5)/2
a1=1.5/(1+q)=1.5/[1+(1±√5)/2]=3/(3±√5)