I know I have got a trivial question but I can't find a proper explanation on the internet. In the image below I know that the formula for the cutoff frequency is f = 1/(2*PI*(R1//R2)*C). One way to get the above formula is to find parallel impedance of R2 and C1. Then apply a voltage divider formula for R1 and R2//C1 and then we can derive the cutoff frequency. But I was wondering is there a better way to get this formula by finding the equivalent resistance of R1 and R2 first and then substituting this equivalent resistance into simple RC filter formula? Is there any method that would allow me to calculate the equivalent resistnce of R1 and R2 first and then use standard RC filter formula? Thanks in advance
You can use mesh analysis as alternative, in time domain as well as in s-domain (Laplace).