How Does Phasor Addition Simplify Trigonometric Expressions?

[smallwa]

Homework Statement

Define x(t)=5cos(wt)+5cos(wt+120)+5cos(wt-120)

simplify x(t) into the standard sinusoidal form:x(t)= A cos(wt+phase).Use phasors to do the algebra.

Homework Equations

The Attempt at a Solution

i know it needs to use phasor addition rule.
First,i represent x1(t),x2(t),x3(t) by the phasors,and then add them together
however the result is 0,then i don't know to dothanks a lot

 

[ehild]

Homework Statement

Define x(t)=5cos(wt)+5cos(wt=120)+5cos(wt-120)

Correct x(t), please!


ehild

 

[smallwa]

Correct x(t), please!


ehild

sorry,corrected

 

[ehild]

The result is really zero. So write x(t)=0.

ehild