Find inc/dec interval of the following function:
f(x) = x^4-50x^2+4
f'(x) = 4x^3-100x
4x^3-100x = 0
4x(x^2-25) = 0
4x = 0 ----> x= 0
x^2-25 = 0----> x = 5, x = -5
So, (-5,0,5) are the critical point....
I cannot find the increasing and decreasing intervals, because when I substittue critical points in f(x) to positive or negative, it just give me negative value.
Can you plz help me by giving me the correct answer.