These long thin rods are essentially just infinite lines of charge, through gauss' law, we can get the electric field for an infinite line of charge to be E = 2Kλ/r, where E is the electric field, K is the electrostatic constant (same as 1/(4πε₀) = 9*10⁹), λ is the linear charge density and r is the distance we are from the line of charge. We'll have 2 of these terms, one for each line of charge. Both lines of charge are 1 cm from the origin, so the r's drop out. Then one has a +1 linear charge density and one has a -1 linear charge density. The 2 and the K are constants and won't matter, so we have the electric field cancel out and we get an E field of 0 at the origin. Math looks like this E = 2Kλ/r + 2Kλ/r = 2K(+1)/(1) + 2K(-1)/(1) = 2K - 2K = 0
