Find the set of values of `alpha` in the interval [ `pi/2,3pi/2`], for which the point (`sin alpha, cos alpha`)does not exist outside the parabola `2 y^2 + x - 2 = 0`

Explanation

`2y^2+x-2=0`

`f(x,y)=2y^2+x-2`

`f(0,0)=0+0-2<0`

`f(h,k)=2k^2+h-2<=0`

`2cos^alpha+sinalpha-2<=0`

`2-2sin^2alpha+sinalpha-2<=0`

`sinalpha(2sinalpha-1)>=0`

`alpha in [pi/2,5/6pi]uu[pi,3/2pi]`.