Please do 3rd number its on the trigonometric equation

i can see that the thiird question is quite tricky indeed. we need to OBSERVE that root3cosx+sinx

or root3cosx+sinx – 2however, root3cosx+sinx – 2 should be greater than zero for the under root sign to make sense.. so, root3cosx+sinx>=2. these both conditions can be true iff root3cosx+sinx=2

or sin(x+pi/3)=1=sin(pi/2)

or x= n*pi+(-1)^n*(pi/2) – pi/3