Am stuck on these : three similar charges:+8.5micro coloumbs are situated around the corner of an equilateral triangle of side 10cm.. calculate the force on each charge in magnitude and direction...
I have calculated the force due to 2 charges since it is the same for all three.. and I got 65.03N. I don't know were to go from here...

I don't know what equation you are using, but the force should be the same for all 3. And you know they each at on a point in an equilateral triangle, of 60 degrees at each angle.

f = workdone x distance. We have them working at angles now, so you might need to figure out the component of the workdone per charge that would work in the direction of it's neighbouring charge.

You have calculated the repulsive force between any two of the charges. So far so good. Next step is to add up the forces acting on any of the charges vectorally to get the total force acting on it. From the attached you should be able to see that for charge A the horizontal components of the force due to charges B and C cancel out, and the vertical components add. So the total force acting on A is the sum of the two vertical components. The total forces acting on charges A, B, and C are all equal in magnitude (due to symmetry), although in differing directions.

@ebaines, thanks, totally understand. It.. hav gotten the answer...
@serious student, thanks for answering