Giá trị x thỏa mãn −8x2+50=0- 8x^{2} + 50 = 0−8x2+50=0là:
x=254x = \dfrac{25}{4}x=425
x=52x = \dfrac{5}{2}x=25
x=−52x = \dfrac{- 5}{2}x=2−5
x=±52x = \pm \dfrac{5}{2}x=±25
Đáp án: <p><span data-type="math-inline" data-latex="x = \pm \dfrac{5}{2}">$x = \pm \dfrac{5}{2}$</span></p>
Phương pháp giải:
Nếu A = B2 thì A = B hoặc A = -B
Lời giải chi tiết:
Ta có:
−8x2+50=0⇔8x2=50⇔x2=508=254⇔x2=(±52)2⇔[x=52x=−52\begin{array}{l} {- 8x^{2} + 50 = 0} \\ \left. \Leftrightarrow 8x^{2} = 50 \right. \\ \left. \Leftrightarrow x^{2} = \dfrac{50}{8} = \dfrac{25}{4} \right. \\ \left. \Leftrightarrow x^{2} = \left( {\pm \dfrac{5}{2}} \right)^{2} \right. \\ \left. \Leftrightarrow\left\lbrack \begin{array}{l} {x = \dfrac{5}{2}} \\ {x = - \dfrac{5}{2}} \end{array} \right. \right. \end{array}−8x2+50=0⇔8x2=50⇔x2=850=425⇔x2=(±25)2⇔x=25x=−25
Vậy x=±52x = \pm \dfrac{5}{2}x=±25
