Question

Bai13: Tim cac gia tri xde bieu thuc sau nhan gia tri am:

a)9-3x b) (2x-4).(x+5) c)\(\dfrac{x+4}{x-2}\)

Answer 1

a)\(9-3x< 0\)

\(9< 3x\)

\(x>3\)

b)\(\left(2x-4\right)\left(x+5\right)< 0\)

\(\Leftrightarrow2x-4>0\Rightarrow2x>4\Rightarrow x>2\)

\(x+5< 0\Rightarrow x< -5\)

\(2< x< -5\)

\(x\in\left\{\varnothing\right\}\)

\(\Leftrightarrow2x-4< 0\Rightarrow2x< 4\Rightarrow x< 2\)

\(x+5>0\Rightarrow x>-5\)

\(-5< x< 2\)

\(x\in\left\{-4;-3;-2;-1;0;1\right\}\)

c)

\(\dfrac{x+4}{x-2}\in Z^-\)

\(\Leftrightarrow x+4< 0\Rightarrow x< -4\)

\(x-2>0\Rightarrow x>2\)

\(2< x< -4\)

\(x\in\left\{\varnothing\right\}\)

\(\Leftrightarrow x+4>0\Rightarrow x>-4\)

\(x-2< 0\Rightarrow x< 2\)

\(-4< x< 2\)

\(x\in\left\{-3;-2;-1;0;1\right\}\)