\magnification=\magstep1


$$
{\rm period\ \ } P \quad = \quad {{1}\over{f}}
$$

$$
t_1 \quad = \quad {{L}\over{v}}
$$

$$
t_2 \quad = \quad {{L}\over{v}}
$$

$$
t_{\rm roundtrip} \quad = \quad t_1 \ + \ t_2 \quad  = \quad {{2 L}\over{v}}
$$

$$
y_1(x, t) \quad = \quad A \thinspace \sin(kx + \omega t)
$$

$$
y_2(x, t) \quad = \quad A \thinspace \sin(kx - \omega t)
$$

$$
\sin(\alpha) \ + \ \sin(\beta) \quad = \quad 
   2 \thinspace \sin{\left( {{\alpha + \beta}\over{2}} \right)}
     \thinspace \cos{\left( {{\alpha - \beta}\over{2}} \right)}
$$

$$
v \quad = \quad \sqrt{{T}\over{\mu}} 
$$


\bye

