Question

帮忙看一下这题

Answer 1

如图

Answer 2

图

Answer 3

s3=6,a1+a1q+a1q^2=6
a1(1+q+q^2)=6
a7+a8+a9=24
a1q^6+a1q^7+a1q^8=24
a1q^6(1+q+q^2)=24
q^6*6=24
q^6=4
q^3=2
S15=a1+a2+a3+a4+a5+a6+a7+a8+a9+a10+a11+a12+a13+a14+a15
=(a1+a2+a3)+(a4+a5+a6)+(a7+a8+a9)+(a10+a11+a12)+(a13+a14+a15)
=a1(1+q+q^2)+a4(1+q+q^2)+a7(1+q+q^2)+a10(1+q+q^2)+a13(1+q+q^2)
=(1+q+q^2)(a1+a4+a7+a10+a13)
=(1+q+q^2)(a1+a1q^3+a1q6+a1q9+a1q12)
=a1(1+q+q^2)(1+q^3+q^6+q^9+q^12)
=6(1+2+4+8+16)
=186

Answer 4

如图