+0

# what is the vertex of x^2+8x+5

0
302
1

what is the vertex of x^2+8x+5

Findthe number that exmpletes the square    x^2 + 18+ ____   and x^2-5x+_______

Guest Oct 11, 2014

#1
+85759
+5

y = x^2+8x+5

In the form y = ax^2 + bx + c, the x coordinate of the vertex is given by x = -b/2a

So here, a = 1 and b = 8

So  x = -8/2(1) = -4

And to find the y coordinate of the vertex, we just put the value for x back into the function.....so we have (-4)^2 + 8(-4) + 5 = 16 - 32 + 5 = -16 + 5 = -11

So the vertex is (-4, -11).....

-------------------------------------------------------------------------------------------------

To answer the other two questions

x^2 + 18x + _____

Just take 1/2 of the coefficient on the x variable and square the resulting value.  Thus (1/2)18 = 9.....and 9^2 = 81. Thus, 81  is the number needed to complete the square (ensure a "perfect square trinomial)

For the second one, we have (1/2)(-5) = (-5/2)   and (-5/2)^2  = 25/4

CPhill  Oct 11, 2014
Sort:

#1
+85759
+5

y = x^2+8x+5

In the form y = ax^2 + bx + c, the x coordinate of the vertex is given by x = -b/2a

So here, a = 1 and b = 8

So  x = -8/2(1) = -4

And to find the y coordinate of the vertex, we just put the value for x back into the function.....so we have (-4)^2 + 8(-4) + 5 = 16 - 32 + 5 = -16 + 5 = -11

So the vertex is (-4, -11).....

-------------------------------------------------------------------------------------------------

To answer the other two questions

x^2 + 18x + _____

Just take 1/2 of the coefficient on the x variable and square the resulting value.  Thus (1/2)18 = 9.....and 9^2 = 81. Thus, 81  is the number needed to complete the square (ensure a "perfect square trinomial)

For the second one, we have (1/2)(-5) = (-5/2)   and (-5/2)^2  = 25/4

CPhill  Oct 11, 2014

### 32 Online Users

We use cookies to personalise content and ads, to provide social media features and to analyse our traffic. We also share information about your use of our site with our social media, advertising and analytics partners.  See details