1. The problem statement, all variables and given/known data The value of g at a point P inside the earth and at another point Q outside the earth is g/2. Maximum possible distance in terms of radius of earth between P and Q is? (g being the acceleration due to gravity on the surface). 2. Relevant equations gh = (1+h/r)-2g gd = (1-d/r)g 3. The attempt at a solution I don't understand what maximum distance is. The value of g reduces whether we go above or below the earths surface and there is only one point above and below that correspond to g/2 and so there is only one distance between those two points. How does maximum distance come into this? Just using the formulas I get: d= R/2 h = R(√2-1) or -R(√2+1) // what does that negative sign actually mean in the second one? Distance between the two points = -(2√2+1)R/2 or (2√2-1)R/2 // again a negative sign. And I suppose maximum means I should choose the first and the answer is right. But I just don't get what the answer means. How can there be more than one distance between P and Q? What do those negative signs mean? Please point out where my understanding is flawed.