+0  
 
-2
99
5
avatar+1164 

Have no idea how to solve this

RainbowPanda  Feb 20, 2018
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5+0 Answers

 #1
avatar+938 
+2

Tell me if you need an explanation. 

Julius  Feb 20, 2018
 #2
avatar+1164 
+1

I need an explanation

RainbowPanda  Feb 20, 2018
 #3
avatar+938 
+3

KK: 

To find the axis of symmetry you use the formula: x= -b/2a 

Once you find the axis of symmetry you can plug into the original formula to find the y value. Since the axis of symmetry is the x value of the vertex. 

Julius  Feb 20, 2018
 #4
avatar+86622 
+3

In the form

 

y  =  ax^2  + bx + c

 

The x coordinate of the vertex  is  given  by      -b / [2a]

 

So....we have

 

y  = -2x^2 + 28x  -  18       ......    b  = 28     a   =  -2

 

So...the x coordinate of the vertex  is given by

 

-(28) / [ 2 * -2]   =   -28 / -4   =  7

 

So  to find the y coordinate of the vertex...sub this value back into the function

 

-2(7)^2  + 28(7)  -  18   =

-98 +  196 - 18  =

80

 

So....the vertex  is  ( 7, 80)

 

This is a  vertical parabola    ....the  axis  of symmetry  is just   

 

x    =  the x coordinate of the vertex

 

x  =  7 

 

Here's the graph :  https://www.desmos.com/calculator/wcucis6wzt

 

 

cool cool cool

CPhill  Feb 20, 2018
 #5
avatar+1164 
+1

Wow tysm! This really helped ^-^

RainbowPanda  Feb 20, 2018

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