Question

As coordenadas do vértice da função y = - x ² + 4x +5 é:
a) V (5, -1)           b) V (-1, -5)            c) V (2,9)         d) V (0,0)

Answer 1

$y=-x^2+4x+5$

$x_v=\dfrac{-b}{2a}$

$x_v=\dfrac{-4}{2(-1)}=2$

$y_v=\dfrac{-\Delta}{4a}$

$\Delta=4^2-4\cdot(-1)\cdot5=16+20=36$

$y_v=\dfrac{-36}{4(-1)}=9$

$V(2,9)$

Alternativa C