Відповідь:

[tex]z_{1}[/tex] = -3

[tex]z_{2}[/tex]= [tex]\frac{1}{7}[/tex]

Пояснення:

Verified answer

[tex]\displaystyle\bf\\7z^{2} +21z-(z+3)=0\\\\7z^{2}+21z-z-3=0\\\\7z^{2}+20z-3=0\\\\D=20^{2} -4\cdot 7\cdot(-3)=400+84=484=22^{2} \\\\\\z_{1} =\frac{-20-22}{14} =\frac{-42}{14} =-3\\\\\\z_{2} =\frac{-20+22}{14}=\frac{2}{14} =\frac{1}{7}[/tex]