(tan x + cot x) sin x * cos x is 1
(tan x + cot x) sin x * cos x
= (tan x + 1 / tan x) sin x * cos x because cot x = 1 / tan x
= (((tan x) ^2 + 1) / tan x) sin x * cos x because (tan x) ^2 +1= (sec x) ^2
= (sin x / cos x) tan x
= tan x / tan x
= 1
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