Answer:
(-2,2)
Step-by-step explanation:
g(x)=x^2-21
-5=x^2-21
0=x^2-16
0=x^2-4^2
0=(x+2)(x-2)
Either,
x=-2 or x=+2 so the interval are [-2,2]
And if it ask for boundary and say the interval is increasing or decreasing we can write the 3 interval ie. (-infinity,-2)(2,-2)(-2,infinity).
