∫ 1/((4(cos x)^2)-((sin x)^2)) dx
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∫ 1/((4(cos x)^2)-((sin x)^2)) dx
请问这题要如何解答呢?
请问这题要如何解答呢?
![∫ 1/((4(cos x)^2)-((sin x)^2)) dx](/uploads/image/z/17592083-35-3.jpg?t=%E2%88%AB+1%2F%28%284%28cos+x%29%5E2%29-%28%28sin+x%29%5E2%29%29+dx)
解题思路:可将分子分母同时除以(cos x)^2,后采用第一换元积分法(即凑微分法)处理:
∫1/[4(cos x)^2 - (sin x)^2] dx
= ∫(secx)^2 / [4 - (tan x)^2] dx
= ∫1 / [4 - (tan x)^2] d(tanx)
= 1/4 ∫[1 / (2 + tan x) + 1 / (2 - tan x)] d(tanx)
=1/4 (ln|2 + tan x| - ln|tan x - 2|) + C
=1/4 ln|(tan x + 2)/(tan x - 2)| + C
∫1/[4(cos x)^2 - (sin x)^2] dx
= ∫(secx)^2 / [4 - (tan x)^2] dx
= ∫1 / [4 - (tan x)^2] d(tanx)
= 1/4 ∫[1 / (2 + tan x) + 1 / (2 - tan x)] d(tanx)
=1/4 (ln|2 + tan x| - ln|tan x - 2|) + C
=1/4 ln|(tan x + 2)/(tan x - 2)| + C