Let $f(x) = 3x^5 - 10x^3 + 15x + a$, where $a$ is some constant. (a) (2 points) Prove that, regardless of the value $a$, $f'(x) > 0$ for all $x$ in $(-1, 1)$. (b) (2 points) Prove that, regardless of the value $a$, the equation $f(x) = 0$ does not have two distinct roots in $[-1, 1]$.
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