\magnification=\magstep2


$$
  \vec{F} \quad = \quad m \vec{a} \quad = \quad m { {d^2 {\vec{x}}}\over{dt^2} }
$$

$$
  m { {d^2 {\vec{x}}}\over{dt^2} } \quad = \quad - k \vec{x} 
$$
  
$$
  { {d^2 {\vec{x}}}\over{dt^2} } \quad = \quad - \left ( {{k}\over{m}} \right )  \thinspace \vec{x}  
$$

\bye
