$0.$ A wind tunnel has a $1$@m$2$

$,6-$m$-$long test section in which air at standard sea$-$level conditions

moves at $50$ m$>$s$.$ It is planned to let the walls diverge slightly $($slant outward$)$ to compensate

for the growth in boundary$-$layer displacement thickness, and thus maintain a constant area

for the inviscid flow. This allows the free$-$stream velocity to remain constant. At what angle

should the walls diverge to maintain a constant velocity between x $=0\mathrm{.}5$ m and x $=5$ m$?$