1 câu trả lời
a) `\sqrt{7-4\sqrt{3}}-\sqrt{(7-2\sqrt{3})^2}`
`=\sqrt{(2-\sqrt{3})^2}-\sqrt{(7-2\sqrt{3})^2}`
`=|2-\sqrt{3}|-|7-2\sqrt{3}|`
`=2-\sqrt{3}-7+2\sqrt{3}`
`=-5+\sqrt{3}`
b) `\sqrt{x+5}=3` `(x>=-5)`
⇔`x+5=9`
⇔`x=4` `(tm)`
Vậy `S={4}`
c) `\sqrt{(3-4x)^2}=3` `(x∈R)`
⇔`|3-4x|=3`
⇔\(\left[ \begin{array}{l}3-4x=3\\3-4x=-3\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=0(tm)\\x=\dfrac{3}{2}(tm)\end{array} \right.\)
Vậy `S={0,3/2}`
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