Answer: any negative value
Explanation:
g(x)= ax², inc on x<0 & dec on x>0
Firstly we need to get the derivative of g(x)
g'(x)=2ax
for inc interval g'(x) should be +ve
x<0 (i.e. x= -ve), then a must be -ve
for dec interval g'(x) should be +ve
x>0 (i.e. x= +ve), then a must be -ve
so in both cases a must be a negative constant