If I have the second order differential equation

y'' + y = 0

The auxilliary equation is

m^2 + m = 0

The two solutions are therefore

m = 0, -1

so

y = A*exp(0*x) + B*exp(-1*x)

Is this correct?

My notes say the solution is

y = C1*cos(x) + C2*sin(x)

can anyone explain please