# Calculating Vrms

Tags:
1. Nov 22, 2016

### kostoglotov

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

Shouldn't I use $V_{rms} = \sqrt{\frac{1}{T}\int_T v^2 dt}$?

Which would be

$$\sqrt{\frac{100}{2\pi}\int_0^{2\pi/100}(20+60cos(100t))^2dt}$$

This equals $\approx 79.88 V$

The answer is given as $\approx 46.9V$ and the solution manual shows the following working

$$\sqrt{20^2 + \frac{60^2}{2}}$$

Why do they apply that solution and not the one I used?

2. Nov 22, 2016

### Staff: Mentor

You might want to check your integration. I find that the integral matches the manual's result.