`y(x) = (1/x) + sqrt(cos(x))` .
cos(x) must be >=0 and cos(x) < 0 for `pigtxgtpi/2` ` `(at the right neighborhood of `pi/2` ). So there can be only the left derivative.
Check that `y(pi/2) = 2/pi` :
`cos(pi/2) = 0` and `y(pi/2) = 2/pi + 0 = 2/pi` .
Next, find the derivative of y:
`y'(x) = -(1/x^2) + (1/2)*(cos(x))^(-1/2)*(-sin(x))` .
(`1/x^2` is finite, `sin(x)` is finite and `(cos(x))^(-1/2)-gt+oo` )
and therefore the tangent line is vertical, its equation is `x=pi/2` .
The graph is here: https://www.desmos.com/calculator/4owqqw7egh