Ответ:

[tex]b_1 = \dfrac{9}{14}\\b_2 = -\dfrac{9}{14}[/tex]

Объяснение:

[tex]\dfrac{7}{9}b^2-\dfrac{9}{28} = 0[/tex]

[tex]\dfrac{7}{9}b^2=\dfrac{9}{28}[/tex]

[tex]b^2=\dfrac{9}{28} \div\dfrac{7}{9}[/tex]

[tex]b^2=\dfrac{9}{28} \cdot\dfrac{9}{7}[/tex]

[tex]b=\pm\sqrt{\dfrac{9\cdot 9}{4\cdot 7 \cdot7}} = \pm\dfrac{9}{2 \cdot 7}= \pm\dfrac{9}{14}[/tex]

[tex]b_1 = \dfrac{9}{14}[/tex]

[tex]b_2 = -\dfrac{9}{14}[/tex]