Question

7x²-21=0
помогите пожалуйста даю 40 балов

Answer 1

$\displaystyle\bf\\7x^{2} -21=0 \ |:7\\\\x^{2} -3=0\\\\x^{2} -(\sqrt{3} )^{2} =0\\\\\Big(x-\sqrt{3} \Big)\cdot\Big(x+\sqrt{3} \Big)=0\\\\\\\left[\begin{array}{ccc}x-\sqrt{3}=0 \\x+\sqrt{3} =0\end{array}\right \ \ \ \Rightarrow \ \ \ \left[\begin{array}{ccc}x_{1} =\sqrt{3} \\x_{2} =-\sqrt{3} \end{array}\right\\\\\\Otvet \ : \ \sqrt{3} \ \ ; \ \ -\sqrt{3}$