To prove 2sinx+2cosx > 2(1-1/
)
Let y = 2sinx+2cosx
Differentiating both the sides we obtain
dy/dx = Sin x . Cos x . 2sinx -1 - Cos x . Sin x . 2cosx - 1
For maxima or minima
dy/dx = 0
or Sin x . Cos x . 2sinx -1 - Cos x . Sin x . 2cosx - 1 = 0
or Sin x . Cos x . 2sinx -1 = Cos x . Sin x . 2cosx - 1
or 2sinx -1 = 2cosx - 1
or Sin x - 1= Cos x - 1
or Sin x = Cos x
which is possible when x = pi / 4
or Sin x = Cos x =1 / 
Thus for Sin x = Cos x =1 / 
y = 2sinx+2cosx = 2.21/
This value is either maxima or minima, but second derivative test shows that it is minima,
(another way is that when x = 0, y = 3 which is greater than 2.21/
Hence later is minima)
Thus y > or = 2.21/
> 2(1-1/
)
Hence Proved