4 x ex^2 = d/dx [ 2 ex^2 ] = 2 d/dx [ ex^2 ] = 2d/dx{ ∑n=0 [ 1 + x2 + x4 / 2! + x6 / 3 ! + x8 / 4 ! + x10 / 5 ! +....]}
= 2 ∑n=0 [ 2x/1! + 4x3/2! + 6x5/ 3! + 8x7/4! + 10x9/5! +....] =
= 4 ∑n=0 [ x/1! + 2x3/2! + 3x5/ 3! + 4x7/4! + 5x9/5! +....] =
= 4 ∑n=0 [ x2n+1/ n!]