Help in a passive low pass filter

Hi everyone..
Good morning/evening..
I hope you all fine..
I need your help..

I have this RC CIRCUIT
**broken link removed**
Assume the following:
**broken link removed**

I need to find V(out) (magnitude only), in the Phasor domain, in terms of the frequency ω and I need to show that the cutoff frequency of this circuit is 1/RC.

Can any body help me with that..? I will be Grateful.

Yes you show an extremely simple RC lowpass filter. It is simple so its slope is gradual which makes it almost useless as a filter.
Nobody uses the "angular frequency" today.
Your formula for its cutoff frequency is WRONG! It is 1 over 2 pi RC.