Question

设实数x,y满足3≤ xy方≤8,4≤ x方除以y≤9,则x3方除以y4方 的最大值是

Answer 1

3≤ xy^2≤8

1/8≤1/xy^2≤1/3 (1)

4≤ x^2/y≤9

16≤ x^4/y^2≤81 (2)

(1)*(2)得

2≤ x^3/y^4≤ 27