Question

Answer 1

\(\Leftrightarrow x^4-5x^2+2x^2-10=0\\ \Leftrightarrow\left(x^2-5\right)\left(x^2+2\right)=0\\ \Leftrightarrow x=\pm\sqrt{5}\)

Vậy chọn D

Answer 2

\(\Leftrightarrow\left[{}\begin{matrix}x^2=5\\x^2=-2\left(loại\right)\end{matrix}\right.\)

\(\Rightarrow x=\pm\sqrt{5}\)

Có 2 nghiệm

Answer 3

Chọn D

Answer 4

D