# Phasor approach question

1. Nov 6, 2007

### hazim

[SOLVED] phasor approach question

using phasor approach, determine the current i(t) in a circuit described by the integrodifferential equation: 4i + 8integral(idt) - 3di/dt = 50cos(2t + 75*)
the right side is so easy to convert to phasor form, but how can i convert the left side or how to solve such a problem?

2. Nov 7, 2007

### premagg

dear it is simple.
just write I=dq/dt.you will get a second order differential equation.
you can solve it easily.

3. Nov 7, 2007

### premagg

also integral(Idt)=q.

4. Nov 9, 2007

### Staff: Mentor

I think the point is to use the phasor format, and realize the for the phasor $$Ae^{i\omega{t}}$$, that

$$d/dt(e^{i\omega{t}})\,=\,i\omega{e^{i\omega{t}}}$$, and

$$\int(e^{i\omega{t}})dt\,=\,\frac{1}{i\omega}{e^{i\omega{t}}}\,=\,\frac{-i}{\omega}{e^{i\omega{t}}}$$