10) \(x^3+4x=4x^2\Leftrightarrow x^3-4x^2+4x=0\Leftrightarrow x\left(x^2-4x+4\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=0\\\left(x-2\right)^2=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x-2=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x=2\end{matrix}\right.\)

11)\(5x\left(x-3\right)-2x+6=0\Leftrightarrow5x\left(x-3\right)-2\left(x-3\right)=0\Leftrightarrow\left(x-3\right)\left(5x-2\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=3\\x=\dfrac{2}{5}\end{matrix}\right.\)

12) \(\left(2x+3\right)^2=\left(x-1\right)^2\Leftrightarrow2x+3=x-1\Leftrightarrow x=-4\)

13) \(x^2-9-4\left(x+3\right)=0\Leftrightarrow\left(x-3\right)\left(x+3\right)-4\left(x+3\right)=0\Leftrightarrow\left(x+3\right)\left(x-7\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=-3\\x=7\end{matrix}\right.\)

1,678 - |x - 0,678| = 0 \(\Leftrightarrow\) |x - 0,678| = 1,678

\(\Leftrightarrow\) x - 0,678 = 1,678 \(\Leftrightarrow\) x = 2,356

Hoặc x - 0,678 = -1,678 \(\Leftrightarrow\) x = -1

She went to her grandparent's house by bus.

C

C. Khối lượng riêng

a/ Br hoá trị I, S hoá trị II, C hoá trị IV

B/ Fe hoá trị III, Cu hoá trị II, Ag hoá trị I

Câu 16:

tan55^o = \(\dfrac{AB}{16}\) \(\Rightarrow\) AB = tan55^o.16 \(\approx\) 23 (m)

Câu 17:

sin68^o = \(\dfrac{AC}{16}\) \(\Rightarrow\) AC = sin68^o.16 \(\approx\) 14,8 (m)

\(\dfrac{2}{5}\sqrt{25x-50}=6\)

\(\Leftrightarrow\dfrac{2}{5}\sqrt{25\left(x-2\right)}=6\)

\(\Leftrightarrow2\sqrt{x-2}=6\)

\(\Leftrightarrow\sqrt{x-2}=3\)

\(\Leftrightarrow x-2=9\)

\(\Leftrightarrow x=11\)

cosABC = \(\dfrac{AB}{BC}\) \(\Rightarrow\) cos65^o = \(\dfrac{AB}{4}\) \(\Rightarrow\) AB = cos65^o.4 = 1,69 (m)

Câu B