Mathematics in senior three, such as why the answer to the eighth question made by derivative is different from the standard answer. After derivative, there is only a in the molecule, so it is not that A is greater than or equal to 0. y= 1-a/(x+a)

y'=a/(x+a)^2

(x+a)^2>； 0, so you need a≥0, and your first step is correct.

But obviously this is not enough. Because the topic requirement is (-2, +∞), this is a continuous interval.

Therefore, the possibility of discontinuity must be ruled out.

Obviously, the discontinuity of this function is x =-a.

So there is -a≤-2.

a≥2