∫ π / 4 π / 3 ( tan x ( ln ( sin x ) ) 1 + ln ( cos x ) tan x ) d x
If the above integral equals to z , z ∈ C , where C denotes the set of complex numbers, evaluate the value of ∣ z ∣ upto three correct places of decimals.
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@Satyajit Mohanty I don't think that your last explanation was the suitable ...
What if the integral was:
∫ 8 π 4 π tan x ( ln ( 2 sin x ) ) d x ? ?
Do you think the answer is complex?
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Nopes. I'm not talking about generalizations. I'm talking about this particular integral.
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Yes even your particular integral, it is real because the antiderivative of x 1 is ln ∣ x ∣ .
Not because of the applied difference :)
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∫ π / 4 π / 3 ( tan x ( ln sin x ) 1 + ln cos x tan x ) d x
= ∫ π / 4 π / 3 ( ( ln ( ln sin x ) ) ′ − ( ln ( ln cos x ) ) ′ ) d x
= ( ln ( ln ( sin x ) ) − ln ( ln ( cos x ) ) ) ∣ ∣ ∣ ∣ ∣ π / 4 π / 3
= ln ( ln ( 2 3 ) ) − ln ( ln ( 2 1 ) )
= ln ⎣ ⎢ ⎢ ⎢ ⎢ ⎡ ln ( 2 1 ) ln ( 2 3 ) ⎦ ⎥ ⎥ ⎥ ⎥ ⎤ ≈ − 1 . 5 7 2 and thus, it's modulus is 1 . 5 7 2 .
Why did we suppose that the value of the integral might be a non-real (complex) entity? The answer is right below.
You can see that both
ln ( ln ( 2 3 ) ) and ln ( ln ( 2 1 ) )
are non-real (complex) numbers, but then, we have
[ ln ( ln ( 2 3 ) ) − ln ( ln ( 2 1 ) ) ] = ln ⎣ ⎢ ⎢ ⎢ ⎢ ⎡ ln ( 2 1 ) ln ( 2 3 ) ⎦ ⎥ ⎥ ⎥ ⎥ ⎤
as a real number.