Mark M. answered 11/01/19
Retired math prof. Calc 1, 2 and AP Calculus tutoring experience.
∫eudu = eu + C
Let u = (1/2)x. Then du = (1/2)dx. So, dx = 2du.
∫e(1/2)xdx = ∫eu(2du) = 2∫eudu = 2eu + C = 2e(1/2)x + C
In general, for any constant k≠0, ∫ekxdx = (1/k)ekx + C.