Bài 5:
a) Đặt P(x)=0
\(\Leftrightarrow5x-10=0\)
\(\Leftrightarrow5x=10\)
hay x=2
b) Đặt Q(x)=0
\(\Leftrightarrow x^3-5x=0\)
\(\Leftrightarrow x\left(x-\sqrt{5}\right)\left(x+\sqrt{5}\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x=\sqrt{5}\\x=-\sqrt{5}\end{matrix}\right.\)