i need help

i need help

2z^2-11z-21

As function with zeros is 2z^2-11z-21

$f(z)=2z^2-11z-21=0$

$z = {-b \pm \sqrt{b^2-4ac} \over 2a}$

$z = {11 \pm \sqrt{121+1684} \over 4}$

$z=\frac{11\pm42.485}{4}$

$z_1=13.371\\z_2=-7.871$

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