Verify that the indicated function is an explicit solution of the given differential equation. Assume an appropriate interval I of definition for each solution

1. 2y' + y = 0; y = e^-x/2

2. dy/dt + 20y = 24; y – 6/5 – 6/5 e^-20t

3. y'' – 6y' + 13y = 0; y = e^3x cos 2x

4. y'' + y = tan x; y = -(cos x) ln (sec x + tan x)