a7=a1q^6
6=a1*(-√2/2)^6
6=a1*(1/2)^3
a1*1/8=6
a1=48
a4=a2q^2
1/4=3*q^2
q^2=1/12
q=±√3/6
a2=a1q
a1=a2/q
a1=±6√3
(a3)^2=a2*a4
(a3)^2=3*1/4
(a3)^2=3/4
a3=±√3/2
a3=3,a6=-81/8
a6=a3q^3
-81/8=3q^3
q^3=-27/8
q=-3/2
a7=a6q=-81/8*(-3/2)=243/16
a2×a10+a4×a8=20,求a6²
a6²+a6²=20
2a6²=20
a6²=10