1. The problem statement, all variables and given/known data -Electron has 3.00 MeV (or 4.8*10^-13 Joules) -it's relativistic -finding λ. 2. Relevant equations h=6.63*10^-34 λ=h/p (obviously) And I'm not sure if they're needed, but the relativistic eq's are: KE = mc^2/sqrt(1-(v/c)^2) p = mv/sqrt(1-(v/c)^2) I'm not sure if this one applies to relativistic speeds: E = hc/λ 3. The attempt at a solution Attempt 1: E = hc/λ 4.8E-13 = (6.63E-34)(3E8)/λ λ = (6.63E-34)(3E8)/(4.8E-13) λ = 4.14E-13 m BUT answer key says 3.58E-13 If you could help, that would be great. Sorry if it's too long, and I'm a little unfamiliar with relativistic eqn's so forgive me if I screwed up on them.