I haven't seen her since three moths ago

C

a, ⇒ (2x - 3)² = 49

    ⇒  (2x - 3)² = \(\left(\pm7\right)^2\)

    ⇒ \(\left[{}\begin{matrix}2x-3=7\\2x-3=-7\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}2x=10\\2x=-4\end{matrix}\right.\)\(\Rightarrow\left[{}\begin{matrix}x=5\\x=-2\end{matrix}\right.\)

b, ⇒ 2x.(x - 5) + 7.(x - 5) = 0

    ⇒ (x - 5).(2x + 7)  = 0

    ⇒ \(\left[{}\begin{matrix}x-5=0\\2x+7=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=5\\2x=-7\end{matrix}\right.\)\(\Rightarrow\left[{}\begin{matrix}x=5\\x=-\dfrac{7}{2}\end{matrix}\right.\)

c, ⇒ x² - 5x + 2x - 10 = 0

    ⇒ (x² - 5x) + (2x - 10) = 0

    ⇒ x.(x - 5) +2.(x - 5)    = 0

    ⇒ (x - 5).(x + 2)=0

    \(\Rightarrow\left[{}\begin{matrix}x+2=0\\x-5=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=-2\\x=5\end{matrix}\right.\)

a, x² - 4 = x² - 2² =(x - 2).(x + 2)

b, 9a² - b² = (3a)² - b² = (3a - b).(3a + b)

c, x³ + 27 = x³ + 3³ =(x + 3).(x² - 3x + 9)

d,8b³ - 125 = (2b)³ - 5³ = (2b - 5).(4b² + 10b + 25)

Hợp chất: MgO, NaCl, BaCO₃

còn lại là đơn chất nhá

x là chiều dài đúng ko????

Nếu x là chiều dài thì chọn B nhá

sits / reads / goes/ watches/ brushes/ listens/ walks/ fixes/ hears /plays /studies/ repeats 

Fe₂O₃