# Electrostatic algebra

1. Feb 3, 2010

### spiderlegs

1. The problem statement, all variables and given/known data

I have a homework question on electrostatic seesaws. My problem is the algebra.

2. Relevant equations

I have been following another example and any guidance to help me proceed would be great.

0= (2q Q)/(4πε_o r²)+(q Q)/(4πε_o r²)-m
0= (3q Q)/(4πε_o r²)-m
m=(3q Q)/(4πε_o r²)

I don't understand line 2. I don't understand how part of the equation has cancelled out. I know there is a step missing so could anyone point me in the right direction.

3. The attempt at a solution

2. Feb 3, 2010

### CompuChip

There is no step missing.

There are two fractions which are the same, therefore they can be added:
$$\frac{2x}{y} + \frac{x}{y} = \frac{3x}{y}$$

3. Feb 3, 2010

### spiderlegs

Of course! Thank you compuchip x