Đáp án:
Giải thích các bước giải:
`c) (x-2/3)^2-1=8.`
`⇒ (x-2/3)^2=8+1.`
`⇒ (x-2/3)^2=9.`
`⇒ (x-2/3)^2=(±3)^2.`
$\text{⇒ \(\left[ \begin{array}{l}x-\dfrac{2}{3}=3.\\x-\dfrac{2}{3}=-3.\end{array} \right.\)}$
$\text{⇒ \(\left[ \begin{array}{l}x=3+\dfrac{2}{3}.\\x=-3+\dfrac{2}{3}.\end{array} \right.\)}$
$\text{⇒ \(\left[ \begin{array}{l}x=\dfrac{9}{3}+\dfrac{2}{3}.\\x=\dfrac{-9}{3}+\dfrac{2}{3}.\end{array} \right.\)}$
$\text{⇒ \(\left[ \begin{array}{l}x=\dfrac{11}{3}.\\x=\dfrac{-7}{3}.\end{array} \right.\)}$
$\text{Vậy x = $\dfrac{11}{3}$; x = $\dfrac{-7}{3}$.}$
`d) 3/4.(2/5)^14÷(4/25)^6.`
`= 3/4.(2/5)^14÷[(2/5)^2]^{6}.`
`= 3/4.(2/5)^14÷(2/5)^12.`
`= 3/4.(2/5)^2.`
`= 3/4. 4/25.`
`= 3/25.`
`e) (1/16)^7÷(1/8)^9`
`= [(1/2)^4]^7÷[(1/2)^3]^9`
`= (1/2)^28÷(1/2)^27`
`= 1/2`
