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What is `int sin x log (tan x) dx` equal to ?A. `cos x log tan x + log tan (x//2) + c`B. `-cos x log tan x + log tan (x//2) + c`C. `cos x log tan x + log cot (x//2) + c`D. `-cos x log tan x + log cot (x//2) + c` |
Answer» Correct Answer - B `int sin x log (tan x) dx` `= - cos x log tan x - int (-cos x) (1)/(tan x). Sec^(2) x dx` `= - cos x log tan x + int (1)/(sin x) dx` `= - cos x log (tan x) + int (1 + "tan"^(2) (x)/(2))/(2 "tan "(x)/(2)) dx` Let `t = "tan"(x)/(2)` `rArr (dx)/(dt) = (2)/(1 + t^(2)) rArr dx = (2)/(1 + t^(2)).dt` So, `- cos x. log (tan x) + int (1 + "tan"^(2) (x)/(2))/(2 "tan"(x)/(2)).dx` `= - cos x. log (tan x) + int (1 + t^(2))/(2t).(2)/(1 + t^(2))dt` `= - cos x log tan x + int (1)/(t) .dt` `= - cos x log tan x + log (t) + c` `= - cos x log tan x + log tan ((x)/(2)) + c` |
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