Đáp án:
Giải thích các bước giải:
\(\begin{array}{l}5.{(x + 1)^2} = 80\\ \Leftrightarrow {\left( {x + 1} \right)^2} = 16\\ \Leftrightarrow x + 1 = 4\,\,\,\,hoac\,\,\,\,x + 1 = - 4\\ \Leftrightarrow x\,\, = 3\,\,\,\,\,\,\,\,\,hoac\,\,\,\,x\, = \,\, - 5 (KO TM) \end{array}\)
Vậy \(x=3\)
Câu 2:
Gọi số đó là: \(\overline {ab} \)
Ta có : \(\overline {ab} :b = 6\,\left( {du\,\,5} \right)\)
\[\begin{array}{l} \Rightarrow \overline {ab} = 6 \times b + 5\\ \Rightarrow 10 \times a + b = 6 \times b + 5\\ \Rightarrow 10 \times a - 5 \times b = 5\\ \Rightarrow 2 \times a - b = 1\\ \Rightarrow 2 \times a = 1 + b\\Voi\,\,\,\,b = 1 \Rightarrow a = 1 \Rightarrow \overline {ab} = 11 \Rightarrow 11:1 = 1\,\,\left( {loai} \right)\\\,\,\,\,\,\,\,\,\,\,b = 2 \Rightarrow 2 \times a = 3 \Rightarrow \left( {Loai} \right)\\\,\,\,\,\,\,\,\,\,\,b = 3 \Rightarrow a = 2 \Rightarrow \overline {ab} = 23 \Rightarrow 23:3 = 7\,\,\left( {du\,2} \right)\,\,\, \Rightarrow Loai\\\,\,\,\,\,\,\,\,\,b = 4 \Rightarrow a = \frac{5}{2} \Rightarrow \left( {Loai} \right)\\\,\,\,\,\,\,\,\,\,b = 5 \Rightarrow a = 3 \Rightarrow \overline {ab} = 23 \Rightarrow 23:3 = 7\,\,\left( {du\,2} \right)\,\,\, \Rightarrow Loai\\\,\,\,\,\,\,\,\,\,b = 6 \Rightarrow a = \frac{7}{2}\,\,\left( {loai} \right)\\\,\,\,\,\,\,\,\,\,b = 7 \Rightarrow a = 4\,\, \Rightarrow \overline {ab} = 47;\,\,\,thu\,\,lai:\,\,47:7 = 6\left( {du\,\,5} \right)\,\, \Rightarrow Thoa\,man\\\,\,\,\,\,\,\,\,b = 8\, \Rightarrow Loai\\\,\,\,\,\,\,\,b = 9 \Rightarrow a = 5 \Rightarrow \overline {ab} = 59 \Rightarrow thu\,\,lai:\,\,\,59:9 = 6\left( {du\,\,5} \right) \Rightarrow Thoa\,\,man\\\,\,\,Vay\,\,\,\,\,\overline {ab} = 47\,\,\,hoac\,\,\,\,\,\overline {ab} = 59\\\,\,\,\,\,\,\,\,\,\end{array}\]
