Question

[Tuyết Ly]

Tìm số nguyên a sao cho:

a) (a²+2)(a²-3)(a²-10)<0

b) ( a+1) (a+3)(a+5) >0

c) (3a +1)( a-2)(a-10) <0

d)(- a⁴ -7)(a-3) (a+1) >0

Answer 1

[Nguyễn Lê Phước Thịnh]

a: \(\Leftrightarrow\left(a^2-3\right)\left(a^2-10\right)< 0\)

\(\Leftrightarrow3< a^2< 10\)

\(\Leftrightarrow\left[{}\begin{matrix}\sqrt{3}< a< \sqrt{10}\\-\sqrt{10}< a< -\sqrt{3}\end{matrix}\right.\)

d: \(\Leftrightarrow\left(a-3\right)\left(a+1\right)< 0\)

hay -1<a<3