$($b$)$ Distinguish between $-$ Alternate depth and sequent depth.

In a rectangular channel $F_1$ and $F_2$ are the Froude numbers corresponding to the alternate depths of a certain discharge. Show that $--$

$(\frac{F_2}{F_1}{)}^{\frac{2}{3}}=\frac{2+F_2^2}{2+F_1^2}$