I have the function
$$f (x) = \cos x - \frac{x^2}{100}$$
$$f'(x) = -\sin x \, -\frac{x}{50}$$
$$f''(x) = -\cos x - \frac{1}{50}$$
and I want to find out how many roots it has, I have tried using calculus and differentiating it. I have tried using Newton's method, and then realized it's not that helpful if I want to find HOW MANY instead of where the roots are.