Question

y'' + y = 0

Can anyone explain to me how the solution to this ODE is c1sin(x)+c2cos(x)?

Answer 1

r^2+1=0
r=i or r=-i

Answer 2

Ohh okay and then thats put into Eulers simplification for complex roots? I see, I was taking that characteristic equation as r^2 + r, my mistake
Thank you

Answer 3

oh yes r^2+r would screw it up here
y''+y'=0
you could do r^2+r=0

Answer 4

Haha kk, thanks