Solution to task 303 from Chertov´s for extramural stud

Solution to task 303 from Chertov´s for extramural stud

303. Two positive point charges Q and 9Q are fixed at a distance d = 100 cm from each other. Determine at what point on the straight line passing through the charges, the third charge should be placed so that it is in equilibrium. Indicate what sign this charge should have in order for the equilibrium to be stable, if the charges can only move along a straight line passing through the fixed charges.