Question

Answer 1

Mik ra đáp án là

a) Th1:x=3

Th2:x=2

b) Th1:x=0

Th2:x=5/2

c) x=2

Answer 2

a) \(\left(2x-1\right)^2-25=0\)

\(\Leftrightarrow\left(2x-1\right)^5=25\)

\(\Leftrightarrow2x-1=5\)

\(\Leftrightarrow x=3\)

b) \(8x^3-50x=0\)

\(\Leftrightarrow2x\left(4x^2-25\right)=0\)

\(\Leftrightarrow2x\left(x^2-\dfrac{25}{4}\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x^2-\dfrac{25}{4}=0\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x=0\\x=\pm\dfrac{5}{2}\end{matrix}\right.\)

c) \(\left(x-2\right)\left(x^2+2x+7\right)+2\left(x^2-4\right)-5\left(x-2\right)=0\)

\(\Leftrightarrow\left(x-2\right)\left(x^2+2x+7+2x+4-5\right)=0\)

\(\Leftrightarrow\left(x-2\right)\left(x^2+4x+6\right)=0\) (*)

mà \(x^2+4x+6=\left(x+2\right)^2+2\ge2\forall x\)

(*) \(\Rightarrow x-2=0\Rightarrow x=2\)