It depends of the value of x
But area under the curve deals with integral
And ∫ 1⁄ (x2 +1) dx = tan-1 (x) (arctan (x))
if x = 0 then tan-1 (0) = 0
but if x = 1, then tan-1 (1) = 450 which is the same as π/4 (pi/4)
Note that sin (x), cos(x) and tan (x) are all positive in the first quadrant.
Hope this helps.