Function f(x)=[4x2+1]x is decreasing for interval
-12,12
-1,1
1,-1
Explanation for the correct option:
Find the decreasing interval of the given function:
f(x)=[4x2+1]x
Differentiate it with respect to x
f'(x)=4–1x2
∵f(x) will be decreasing if f'(x)<0
⇒4–1x2<0
⇒ 1x2>4
⇒ −12<x<12
Thus, the function is decreasing in (−12,12).
Hence, Option ‘A’ is Correct.