Question

O vértice da função y = - x2 - 4x + 5 é:
a) ( - 4, 9 )
b) ( - 2, 4 )
c) ( - 2, -9 )
d) ( - 2, 9 )
e) ( 2, - 9 )
Me ajudem por favor.

Answer 1

Y = - x2 - 4x + 5
Y = x2 + 4x - 5
∆ = 16 + 20
∆ = 36
Xv= - b / 2a

Xv = - 4 / 2
Xv = - 2
Yv = ∆ / 4a
Yv = 36 / 4
Y v = 9
( - 2 , 9)
opção D

Answer 2

Vamos lá:

$y=-x^2-4x+5 \\\\ \Delta = (-4)^2-4.(-1).5 \\\\ \Delta = 16+20 \\\\ \Delta = 36 \\\\ Y_v = - \frac{\Delta}{4a} \\\\ Y_v = - \frac{36}{4.(-1)} \\\\ Y_v = \frac{36}{4} \\\\ Y_v = 9 \\\\ x' = \frac{-(-4)+\sqrt{36}}{2.(-1)} \\\\ x'=\frac{4+6}{-2} \\\\ x'=-\frac{10}{2} \\\\ x'=-5 \\\\ x"=\frac{-(-4)-\sqrt{36}}{2.(-1)} \\\\ x"=\frac{4-6}{-2} \\\\ x"=\frac{-2}{-2} \\\\ x"=1 \\\\ X_v=\frac{-5+1}{2} \\\\ X_v=\frac{-4}{2} \\\\ X_v=-2$

Alternativa D

Espero ter ajudado.