What is the Coulomb's Law formula for calculating point charges?

[logearav]

Homework Statement

The sum of two point charges is 6 micro coulomb. They attract each other with a force of 0.9 Newton, when kept 0.4 m apart in vacuum. calculate the charges.

Homework Equations

since it is attractive force, i formed the equation q₁-q₂= 6 *10⁶ and got the relevant equation for q₂
then we have the coulomb's law f = q1*q2/4 *3.14*epsilon0 *r²
Should i use - q₁q₂ or simply q1*q2 in the coulomb's formula

The Attempt at a Solution

 

[tiny-tim]

hi logearav!

The sum of two point charges is 6 micro coulomb. They attract each other with a force of 0.9 Newton, when kept 0.4 m apart in vacuum. calculate the charges.
…
Should i use - q₁q₂ or simply q1*q2 in the coulomb's formula

what difference does it make? … the magnitude of the result will be the same anyway

(btw, i assume you used q₁ - q₂ (instead of q₁ + q₂) because you were trying to simplify things …

not much point in simplifications if they confuse you later! )

 

[logearav]

Thanks a lot tiny-tim.