1. The problem statement, all variables and given/known data Two spheres of mass m and a third sphere of mass M form an equilateral triangle, and a fourth sphere of mass m4 is at the center of the triangle. The net gravitational force on that central sphere from the three other spheres is zero. (a) What is M in terms of m? (b) If we double the value of m4, what then is the magnitude of the net gravitational force on the central sphere? 2. Relevant equations Fnet = F1,4 + F2,4 + F3,4 F = GMm/r2 3. The attempt at a solution F1,4 = GMm/r2 F2,4 =Gm2/r2 F3,4 =Gm2/r2 Fnet = 0 = F1,4 + F2,4 + F3,4 0 = GMm/r2 + Gm2/r2 +Gm2/r2 0 = Mm + 2m2 Mm = -2m2 M = -2m this is not correct. please help me figure out what i'm doing wrong. thanks.