Find the vertex of the parabola whose equation is y = -2x^2 + 8x - 5.

(2, 3)

(2, 19)

(2, 27)

Question

Find the vertex of the parabola whose equation is y = -2x^2 + 8x - 5.


(2, 3)

(2, 19)

(2, 27)

campbell_st · Answer

an easy method for a quadratic 

$$ax^2 + bx + c $$

is to find the line of symmetry... 

$$x = \frac{-b}{2a}$$

and the vertex is on the line... 

then substitute this value into the equation to find the corresponding y value... 

and then you have the vertex

in your question a = -2 and b = 8

hope it helps

anonymous · Answer

I know that, and I did it, but the answer I got (even after repeating everything numerous times) was the same and apparently it's not right.

campbell_st · Answer

well what did you get for the line of symmetry

x = ?

anonymous · Answer

The answer I got is (2, 15) but obviously that isn't correct lol

campbell_st · Answer

well the x value is correct... 

substituting 

y = -2(2)^2 + 8(2) - 5

y = -8 + 16 - 5

so y = 3

thats my best guess

anonymous · Answer

Thank you.. I'll just go with that then lol

campbell_st · Answer

the x value is correct... the error was just in the substitution and evaluation...

whpalmer4 · Answer

You should figure out why you're making a mistake evaluating $$y = -2(2)^2+8(2)-5$$so that you can avoid that mistake in the future...

anonymous · Answer

I'll deal with the future when it gets here! This question is closed, thanks for the help.