Which Statements Are True?

Calculus Level 3

Of the four statements below, which are true?

I. The equation \(x^4 -3x+ 1 = 0\) has a unique real solution.
II. The equation \(\sin x = x\) has a unique real solution.
III. The equation \(3x^5 - 20x^3 + 60x +16=0\) has a unique real solution.
IV. The equation \(\tan x = x\) has a unique real solution.