Graph the given function. Identify the vertex and the axis of symmetry

y=2x^2+8x+9

I ended up with a vertex of (-2,7) but it should be (-2,1). Can somone show me how to get that?

Question

Graph the given function. Identify the vertex and the axis of symmetry

y=2x^2+8x+9

I ended up with a vertex of (-2,7) but it should be (-2,1). Can somone show me how to get that?

campbell_st · Answer

well the easy way to find the vertex is to 

1. find the line of symmetry

$$x = \frac{-b}{2a}$$

you have b = 8 and a = 2

so

$$x = \frac{-8}{ 2 \times 2}$$

then substitute the answer into the equation... 

so be careful with the substitution 

$$y = 2 \times (-2)^2 + 8 \times (-2) + 9$$

hope it helps

anonymous · Answer

Thank you! :)