We need to take the derivative, which is:
[tex]f'(x) = 10x + 2[/tex]
and see where it is positive (increasing) and negative (decreasing). We see that [tex]f'(x) = 0 at x = -1/5, f'(x) < 0 for x < -1/5, and f'(x) > 0 for x > -1/5[/tex]. Therefore, we have
f(x) increasing: (-1/5, ∞)
f(x) decreasing: (-∞, -1/5)
