# Math Help - sigma

1. ## sigma

please see attached file regarding my problem.

2. Originally Posted by afsaneh
please see attached file regarding my problem.
You have two sums where the index of summation is h, these are different h's (that is they are dummy indices of summation).

Please rethink what you want to do and repost. Alternativly post the real question.

Also, don't post the question in an attachment, we don't like opening attachments. If you can't be bothered to learn to use our LaTeX add-in attach a graphic file.

CB

3. ## sigma

p(t)=v(t)*i(t)
p is the electrical power consumed by a consumer.
voltage:v(t)=vh*sinhwt
current:i(t)=ih*sin(hwt+phih)
h is harminic number of main sin wave.that is from 1 to n=50.
to calculate p(t) we must multiply v(t) and i(t)
sentences with v and i of different h are distortion power that are not my requirement.
sentences with v and i of same h must be involved sin2hwt and cos2hwt that are active power and reactive power.
i want to multiply two sigma and gain active and reactive power.
formula in attached file has an error.first sigma must be v(h)*sin(hwt) and second sigma must be i(h)sin(hwt-phih)
sorry for error.i am too busy and confused.

4. ## formula

$\sum\limits_{h = 1}^N {\sin (h*w*t)*vh}$* $\sum\limits_{h = 1}^N {\sin (h*w*t-phih)*ih}$

5. Originally Posted by afsaneh
$\sum\limits_{h = 1}^N {\sin (h*w*t)*vh}$* $\sum\limits_{h = 1}^N {\sin (h*w*t-phih)*ih}$
The summation indices should be different!

CB

6. i want simple form of equation not the answer of equation.
after multiplying two sigma we will have two type sentences: $\sum\limits_{h=1}^n{\sin(h*w*t)*ih*vh*sin(h*w*t-phi)}$
in ih and vh, h is index.
the other type is not my aim.
in this sentence how can i change sin(h*w*t)*sin(h*w*t-phi) to sin(2*h*w*t) and cos(2*h*w*t)?