Question

(A) 10

(B) −1

(C) 1

(D) 9

(E) −9

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Answer 1

$\sf y = {x}^{2} + 10x + 9$

$\sf 0 = {x}^{2} + 10x + 9$

$\sf {x}^{2} + 10x + 9 = 0$

$\sf \Delta=b²-4ac$

$\sf \Delta = 10² - 4 \cdot 1 \cdot 9$

$\sf \Delta = 100 -36$

$\sf \Delta =64$

$\sf x_{½} = \dfrac{ - b \pm\sqrt{ \Delta } }{2\cdot a}$

$\sf x_{½} = \dfrac{ - 10 \pm\sqrt{64 } }{2\cdot 1}$

$\sf x_{½} = \dfrac{ - 10 \pm8 }{2}$

$\sf x_{1} = \dfrac{ - 10 - 8 }{2} = \dfrac{ - 18}{2} =\red{ - 9}$

$\sf x_{2} = \dfrac{ - 10 + 8 }{2} = \dfrac{ -2}{2} =\red{ - 1}$

$\boxed{\boxed{\sf Letra \: E}}$