Find the vertex of the parabola formed by the following quadratic function: y = x2 + 8x − 4

(a) (-8,-4)

(b) (8, 124)

(c) (4, 44)

(d) (-4, -20)

Question

Find the vertex of the parabola formed by the following quadratic function: y = x2 + 8x − 4 
		
(a) (-8,-4)
		
(b) (8, 124)
		
(c) (4, 44)
		
(d) (-4, -20)

stephstar101 · Answer

The lowest point on this graph is at (-4,-20)

campbell_st · Answer

the line of symmetry passes through the vertex

to find it use

$$x = -\frac{b}{2a}$$

in your question you have 

$$x = -\frac{8}{2\times1}$$

the line of symmetry is x = - 4

substitute x = -4 into the equation to find the y value y = -20

vertex (-4, -20)

an alternative method is complete the square

y = x^2 + 8x + 16 - 20

y = (x + 4)^2 - 20

vertex at (-4, -20)