等比数列中 a7-a12＝15 求a8*a9*a10*a11

题目抄错了,应该是a7a12=15,是相乘,不是相减.
a7a12=15
a7^2q^5=15
a8a9a10a11
=a7^4 q^10
=(a7^2q^5)^2
=15^2
=225