Discover Questions

I need to get an ultrasound not because I'm having a baby but I have a lump on my chest. about much are they? I hope not as much as an MRI? How does anyone know the world is real? Does the sum of (-1)^(n+1)*e^(-n)*n^3 approaching infinity converge or diverge? What equation did Einstein use to show that the speed of light changes subject to the level of gravity? Solve for 0
2x-6/x^3?