SHM- Problem with negative signs

[annms]

I have problems understanding the use of negative signs in SHM. ie. mx''=-kx

Why is there a negative sign for the constant k and what does the negative sign mean?

 

[Doc Al]

The negative sign in Hooke's law tells you that the force is opposite to the displacement from equilibrium. If x is positive, then the force is negative. And vice versa.

The negative sign is not part of the constant k.