提示 sin⁷x + csc³x - cos⁷x - sec³x
= csc³x cos¹⁰x (1 - tan x)f(tan x),
其中, f(t) = 1 + t + 6t² + 4t³ +14t⁴ + 9t⁵ + 19t⁶ + 9t⁷ + 14t⁸ + 4t⁹ + 6t¹⁰ + t¹¹ + t¹² > 0.
= csc³x cos¹⁰x (1 - tan x)f(tan x),
其中, f(t) = 1 + t + 6t² + 4t³ +14t⁴ + 9t⁵ + 19t⁶ + 9t⁷ + 14t⁸ + 4t⁹ + 6t¹⁰ + t¹¹ + t¹² > 0.
