Question

等比数列an中,已知a1乘以a2乘以a3等于1,a2加a3加a4等于四分之7则a1

Answer 1

a1*a2*a3=1. a2+a3+a4=4/7.

~~>a1*a1q*a1q²=1.

a1^3*q^3=1.①

a1q+a1q²+a1q^3=4/7.

a1q(1+q+q²)=4/7②

a1q=1.

1+1/a1+1/a1²=4/7.

1/a1²+1/a1+3/7=0.

1+a1+3/7*a1²=0.

7+7a1+3a1²=0.

然后解方程咯