# Thread: Differential Equation from RLC Circuit

1. ## Differential Equation from RLC Circuit

Can somebody show the missing step/s between (8.18) and (8.19)? The equation comes from a book on electrical circuits.

2. ## Re: Differential Equation from RLC Circuit

Originally Posted by p75213
Can somebody show the missing step/s between (8.18) and (8.19)? The equation comes from a book on electrical circuits.
Try working in reverse, it's just a recognition of evaluating a derivative using a product rule...

3. ## Re: Differential Equation from RLC Circuit

Originally Posted by Prove It
Try working in reverse, it's just a recognition of evaluating a derivative using a product rule...

I see what you mean.

4. ## Re: Differential Equation from RLC Circuit

Just to confirm, being i the imaginary unit, first term should vanish as di/dt=0?

5. ## Re: Differential Equation from RLC Circuit

Originally Posted by rulmismo
Just to confirm, being i the imaginary unit, first term should vanish as di/dt=0?
Most definitely NOT. In electrical engineering, i is current, and j is the square root of minus one, in order to avoid just this confusion. The current i = i(t) is a function of time.