Need help, solving a "Quadratic Functions" or "Graph of Quadratic Function" problem

Question

Hello there! I'm having trouble with this one problem that my teacher gave to me and my classmate.

I hope you can solve it by showing the solution, the construct a table of values, and maybe the graph. Much appreciated if you helped! ^^

Problem ~> y = 2x^2 + 8x - 2

Answer 1

y=2x^2+8x -2 =0

divide by 2

x^2 +4x-1 = 0

x^2+4x = 1

complete the square, add (4/2)^2= 4 to both sides

x^2 +4x +4 = 1+4

(x+2)^2 = 5

take the square root of both sides

x+2 = +/-sqr5

x = -2+sqr5, -2-sqr5

x = about -4.2 or 0.2

It's an upward opening parabola, with vertex =minimum= (-2,-10), y intercept=-2, x=-2 is the axis of symmetry

with x intercepts = 2+sqr5 = zeros, = the solutions

or

with a graphing calculator just find where the graph intersects the x axis. Those x values are the two solutions

x y

-2 -10

0 -2

-4 -2

-1 -8

-3 -8

.2 0 approximately

-4.2 0 approximately