Adding and subtracting 2 AC sinusoidal waveforms graphically and by phasor

Thread Starter


Joined Dec 7, 2014
Please help.
I've been struggling with this all weekend (adding and subtracting 2 AC wave forms - phasor and graphically)and although I am starting to understand little bits, I need help. I have found the worksheets on this web site but still can't seem to work out the answer. The worksheet shows 2 sine waves and then gives the following detail -
What do you suppose the sum of a 1-volt (peak) sine wave and a 2-volt (peak) sine wave will be, if both waves are perfectly in-phase with each other?
Hint: you will need to enter equations into your plotting device that look something like this:
y1 = sin x
y2 = 2 * sin x
y3 = y1 + y2

Even with this, I'm struggling. Then I have to work out the answers by phasor - headache does not come close.
I would appreciate any guidance please.


Joined Feb 24, 2006
If you do the straight substitution
y3 = sin x + 2* sin x
Isn't the answer a mater of simple algebra?

When adding phasors with the same angle, what are you supposed to do?
Shouldn't the answer be the same?
If two things are equal to the same thing, shouldn't they be equal to each other?


Joined Nov 23, 2012
sin(x) + 2*sin(x) = 3*sin(x)
Since x is the same, that indicates they are in phase.

To put one out of phase, add something to x on one signal.

y3 = sin(x) + 2*sin(x+?)