b

a, ⇒ x - 15 =0

    ⇒ x        = 15

b, ⇒ x - 10 = 1

   ⇒  x        = 11

c, \(\Rightarrow\left[{}\begin{matrix}x-5=0\\x-7=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=5\\x=7\end{matrix}\right.\)

d, ⇒ x - 35 = 1

    ⇒ x         = 36

isn't exciting

has collected / was

getting

weren't playing

were built

flowers -> flower

flowers -> flower

câu 1:

a, 6 ng tử canxi

b, 4 ng tử sắt

c, 2 ng tử natri

câu 2

a, 3N    b,   5Cu       c, 8Mg

câu 3:

PTK_{canxi cacbonat}= 40 + 12 + 16.3 = 100 đvC

PTKaxit clohidric = 1 + 35,5 = 36,5đvC

PTK_{muối ăn} = 23 + 35,5 = 58,5đvC

PTK_nước = 1.2 + 16 = 18đvC

= - (x² - 2xy + y² - 9) = - [ (x - y)² - 3² ] = - (x - y - 3).(x - y + 3)

b