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Adnen Khiari
Apr 23, 2021

cool integral

in Video Ideas

integral of sin(ln(x))/x² ( try to use complexe numbers )

2 comments
0
Ian Fowler
Apr 24, 2021  ·  Edited: Apr 24, 2021

[-cos(lnx) - sin(lnx)]/[2x]


I have never used this method before as my "go to" method. It is pretty cool and seems to have worked like a charm. We have to know that for complex z,n (where n is a complex constant) that:

d[z^n]/dz = n*z^(n-1) - it's been a long time since 2nd year complex analysis.


Or more to the point:

int[x^(i-2)]dx = [x^(i-1)]/[i-1]

and just go after the Im part.


For some reason it never occurred to that for real x, x^i has principle value:

x^i = cos(lnx) + i*sin(lnx)

Now that's cool.


At any rate, you have opened a new door for me. Thanks - Ian.

0
Hassan Elghazouani
Jun 02, 2021

can you help me please

0
2 comments