[hwary]

Y=(7-3tan(x/2))^0.5
dY/dX=0.5(7-3tan(x/2))^-0.5 x (0-3/2 sec^2 (x/2)) , when x=90
=0.5(7-3tan45)^-0.5 x -1.5 sec^2 45
=0.5(7-3)^-0.5 x -1.5 x 2
=0.25 x -3 = -0.75

4 x -0.75 - 3 = 0