What is the equation of motion of harmonic oscillator?

Harmonic oscillator

Equation of motion of harmonic oscillator is,
$$ \frac{d^2x}{dt^2}+\frac{k}{m}x=0$$

Frequency of harmonic oscillator is,
$$ \nu = \frac{1}{2\pi} \sqrt{\frac{k}{m}}$$

The energy of a harmonic oscillator is,
$$ E = (n+\frac{1}{2})h\nu$$