The equation as attach below. i have the problem on question (b). i confuse to determine the value ofbecause the i have the ans forpoint of inflection

dy/dx = +ve the ans given is dy/dx = -ve. see the circle which i mark.

for your info, when i substitute x=-2 into dy/dx equation, i have the ans as 1/2 which is a +ve as a ans.

thank in advise