# Modulus of Vector

Discussion in 'Homework Help' started by mo2015mo, Oct 21, 2013.

1. ### mo2015mo Thread Starter Member

May 9, 2013
157
1
Hello guys,,,

How is the modulus of E = √(2a^2) for the written E-vector as attached photo ,,
Is not it should equal = (a) ?? ((by using this identity (cosx)^2+(sinx)^2 = 1 ))
Or there is any mistake by find it ??

2. ### WBahn Moderator

Mar 31, 2012
20,064
5,665
What photo?

So are you saying that the E = √(200a^2) would alos equal (a)?

What does the parens in (a) mean? Is it different than the parens in (2a^2)? If so, how is someone supposed to tell the difference?

3. ### mo2015mo Thread Starter Member

May 9, 2013
157
1
this attached photo

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8.1 KB
Views:
21
4. ### anhnha Well-Known Member

Apr 19, 2012
783
49
I think you are right. However, I would like to be confirmed by someone.

5. ### WBahn Moderator

Mar 31, 2012
20,064
5,665
You are correct. You might consider throwing this text book away.

You basically have the x component is a*cos(θ) and the y component is a*sin(θ). The modulus is the Pythagorean sum of these, so

|E| = √[ (a*cos(θ))^2 + (a*sin(θ))^2 ]

|E| = √[ (a^2)[cos(θ)^2 + sin(θ)^2] ]

|E| = √[ (a^2) ]

|E| = |a|

anhnha likes this.