I do not understand the following derivation. Could somebody please enlighten me:
dx/dt = b - ax
to solve, define a new variable y(t) = x(t) - b/a
since dy/dt = dx/dt, we can derive the equation dy/dt = - ay [*]
since y(t) = y(0)exp(-at) and substituting back to express the solution in terms of x(t)
x(t) = b/a + (x(0) - b/a) exp(-at) [*]
>>>I don't know how they got [*] and then [**].