(a1+a2+...+a10)*q^10= a11+ a12 +.. + a20
所以
a11+ a12 +.. + a20 = S20 - S10 = 75-25 = 50
25 * q^10 = 50
q^10 =2
(a11+ a12 +.. + a20) *q^10 = a21+ a22 + ... +a30
所以
S30 - S20 =(a11+ a12 +.. + a20) *q^10 = 50 * q^10 = 50 *2 =100
S30 = 100 + S20 = 100 +75 = 175你确定没做错吗你自己看吧！