+0  
 
0
33
1
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Please help me. I need to explain the answer in full detail but I don't understand how. Sorry...

Guest Aug 23, 2018
 #1
avatar+88775 
+1

If the   quadratic function opens downward, we will have a negative sign in front of the x^2  term...so we can eliminate the last two answers right away

 

In the form     ax^2  + bx + c, the  x coordinate of the vertex  =  -b / [ 2a]

 

 

Look at answer B.....letting a  = -1   and b  = 4....the x coordinate of the vertex  is

 

-4  / [ 2 * -1 ]   =  -4 / -2   =   2

 

To find the y value associated with this x value, put this "2"  back into the function

 

-(2)^2  + 4(2) +   1   =

 

-4  +   8  +   1    =

 

-4  +  9   =

 

5

 

So....this function  turns downward  and has a vertex  of  (2, 5)

 

Here's a graph to confirm this  :  https://www.desmos.com/calculator/tlavaymezd

 

cool cool cool

CPhill  Aug 23, 2018

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