Câu 1:
b) | x + 2 | + | x² + 2x | = 0
x + 2 + x² + 2x = 0
x ( x + 1) + 2 ( x + 1 ) = 0
( x + 2 ) ( x + 1 ) = 0
Để ( x + 2 ) ( x + 1 ) = 0
⇒ hoặc \(\left[ \begin{array}{l}x+2=0\\x+1=0\end{array} \right.\) ⇔ \(\left[ \begin{array}{l}x=-2\\x=-1\end{array} \right.\)
⇒ Vậy x = -2; x = -1
Câu 2:
b) (1-$\frac{1}{21}$) . (1-$\frac{1}{28}$) . (1-$\frac{1}{36}$). ... (1-$\frac{1}{1326}$)
= $\frac{20}{21}$ . $\frac{27}{28}$ . $\frac{35}{36}$. ... $\frac{1325}{1326}$
= $\frac{40}{42}$ . $\frac{54}{56}$ . ... . $\frac{2650}{2652}$
= $\frac{5 . 8}{6.7}$ . $\frac{6.9}{7.8}$ . ... . $\frac{50.53}{51.52}$
= $\frac{5.53}{7.51}$
= $\frac{265}{357}$
Chúc bạn học tốt!!!
