I am trying to follow along an answer to a particular question and don't understand one of the steps taken. I don't understand how they got from step 3 to step 4? The steps can be seen below.
I think they have divided both sides by $R_1$ which is where the $ \frac{R_2}{R_1}$ comes from. But where does the other $R_1$ go to that is multiplied with $C$?
$ Step1=> R_1 ( C + Ci ) = R_2 ( C + C ) $
$ Step2=> R_1C + R_1Ci = 2R_2C $
$ Step3=> R_1Ci = 2R_2C - R_1C $
$ Step4=> Ci = 2 \frac{R_2}{R_1} C - C $
$ Step5=> Ci = C (2 \frac{R_2}{R_1} - 1 )$
Since $\dfrac{R_1C}{R_1}=C$, it vanishes.