Question

若{AN} 等比数列且A2乘A16=36(1)求A9的值(2)若A4平方+A14平方=100求(A4+A14)平方的值

Answer 1

(1) A2*A16=36

=A9*A9

=A9^2

所以A9=6

(2)A4^2+A14^2=100

(A4+A14)^2=A4^2+A14^2+2A4A14

=100+2A4A14

=100+2*A2*A16

=100+2*36

=100+72

=172