Finding F31x component of electric force between two charges

[Goatscholar18]

Homework Statement

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In this problem I am trying to understand the solution for finding the net force on charge 3 due to charge 1.
However, I am getting stuck already on F31x.

Homework Equations

F=kqq/r^2

The Attempt at a Solution

I found theta by tan-1(0.5/1)=26.565degrees
r= sqrt (1^2+0.5^2) = sqrt (1.25)= 1.118

So I did F31x=[k(3X10-6)(-2X10-9)]/ (1.118^2) = 4.32 X 10^5(cos26.565)=-3.86X10^-5N in the i direction

this is obviously incorrect but I don't understand why please help.

Thank you![/B]

 

[mfb]

I get the same result as you.
The book used 1.25 m as distance instead of the correct $\sqrt{1.25}\, m$.