Question

Tìm x biết :
b) (x − 5) · (x 2 − 16) = 0
c) (−5) · (x − 2015) < 0

d) (3 − x)(x + 6) > 0 

 

Answer 1

\(b,\Leftrightarrow\left(x-5\right)\left(x-4\right)\left(x+4\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=5\\x=4\\x=-4\end{matrix}\right.\\ c,\Leftrightarrow x-2015>0\Leftrightarrow x>2015\\ d,\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}3-x>0\\x+6>0\end{matrix}\right.\\\left\{{}\begin{matrix}3-x< 0\\x+6< 0\end{matrix}\right.\end{matrix}\right.\Leftrightarrow-6< x< 3\)

Answer 2

x=5

Answer 3

b: \(\Leftrightarrow\left[{}\begin{matrix}x=5\\x=4\\x=-4\end{matrix}\right.\)

Answer 4

x∈(2015, ∞)

Answer 5

\(b,\left(x-5\right)\left(x^2-16\right)=0\\ \Rightarrow\left(x-5\right)\left(x-4\right)\left(x+4\right)=0\\ \Rightarrow\left[{}\begin{matrix}x=5\\x=4\\x=-4\end{matrix}\right.\\ c,-5\left(x-2015\right)< 0\\ \Rightarrow x-2015>0\\ \Rightarrow x>2015\)

\(d,\left(3-x\right)\left(x+6\right)>0\\ \Rightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}3-x>0\\x+6>0\end{matrix}\right.\\\left\{{}\begin{matrix}3-x< 0\\x+6< 0\end{matrix}\right.\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x< 3\\x>-6\end{matrix}\right.\\\left\{{}\begin{matrix}x>3\\x< -6\left(vô.lí\right)\end{matrix}\right.\end{matrix}\right.\)

\(\Rightarrow-6< x< 3\)

Answer 6

x∈(-6, 3)