## raheen Group Title Find the holomorphic function f(x+iy) such that Re f(x+iy)= cosh(3y)sin(3x) and f(0)=0 3 years ago 3 years ago

1. hahd Group Title

ugh i havent taken calc yet so i cant do this

2. satellite73 Group Title

cauchy reimann yes?

3. raheen Group Title

yes satellite

4. satellite73 Group Title

so the derivative of this wrt x must be the derivative of the imaginary part wrt y right? the derivative is $3\cos(3x)\cosh(3y)$ integrate wrt y and get $\cos(3x)\sinh(3y)$ i think.

5. satellite73 Group Title

it's been a while. am i on the right track?

6. satellite73 Group Title

you also need the partial wrt y is minus the partial wrt x of the imaginary part. if we are lucky it already is oh and you also need that f(0)=0 i forgot the +C when i integrated

7. satellite73 Group Title

how to you like that? i miracle! it works

8. satellite73 Group Title

so i guess unless i totally screwed this up the answer is $f(x+iy)=\cosh(3y)\sin(3x)+\cos(3x)\sinh(3y)$

9. satellite73 Group Title

think we lost raheen maybe he will be back

10. satellite73 Group Title

rather $f(x+iy)=\cosh(3y)\sin(3x)+i\cos(3x)\sinh(3y)$

11. satellite73 Group Title

i forgot the i part

12. satellite73 Group Title

@raheen look ok?

13. satellite73 Group Title

it does not come with a money guarantee because it has been several years but i think it looks good. you can check cauchy reimann equations for this and see if they work

14. raheen Group Title

satellite you are about to reach , great work I think you did how about using the 2 conditions of C-R then you need to integrate and don forget to find the constant

15. satellite73 Group Title

well i integrated wrt y and got the answer. then i checked that the second equation and it worked. and by inspection you can see that $f(0)=0$

16. satellite73 Group Title

i mean if the C-R equations are going to work, then after i take the derivative wrt x and integrate wrt y , then the second condition $\frac{\delta u}{\delta y}=-\frac{\delta v}{\delta x}$ had better work or else we are screwed. both conditions must hold. but in any case i checked and they do

17. raheen Group Title

that's so great satellite, thank you.

18. satellite73 Group Title

yw

19. Zarkon Group Title

the only thing I would add is that when you integrated with respect to y you don't get C you get some function of x

20. raheen Group Title

Zarkon, thank you, you are right it's C(x)

21. Zarkon Group Title

It doesn't look like it will change the final answer though