已知等比[an]中an>0,a1和a99是方程X²-10X+16=0的两根,则a40×a50×a60=?

题目

已知等比[an]中an>0,a1和a99是方程X²-10X+16=0的两根,则a40×a50×a60=?

答案

a40×a50×a60=a50^3 a1a99=a50^2=a16 an>0 a50=4 a40×a50×a60=a50^3=4^3=64