- #1

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- ( x^2 - 4x + (4/2)^2 ) - 4

= - (x - 2) - 4

Vertex is at (2, -4)

but the vertex is obviously at (2,4)...

what did I do wrong.

- Thread starter Miike012
- Start date

- #1

- 1,011

- 0

- ( x^2 - 4x + (4/2)^2 ) - 4

= - (x - 2) - 4

Vertex is at (2, -4)

but the vertex is obviously at (2,4)...

what did I do wrong.

- #2

Mark44

Mentor

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- 5,782

The error is here. You have actually added -4 inside the parentheses to complete the square, so to keep the expression equal, you need to add + 4.Problem: -x^2 + 4x

- ( x^2 - 4x + (4/2)^2 ) - 4

= - (x - 2) - 4

Vertex is at (2, -4)

but the vertex is obviously at (2,4)...

what did I do wrong.

- #3

- 1,011

- 0

- #4

Mark44

Mentor

- 34,167

- 5,782

-x

= -(x

= -(x

I put in +4 inside the parentheses, but due to the minus sign out front, I have actually added -4, so to balance, I have to add + 4.

= -(x - 2)

- #5

HallsofIvy

Science Advisor

Homework Helper

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[tex]-(x^2- 4x)= -(x^2- 4x+ 4- 4)= -(x^2- 4x+ 4)-(-4)= -(x- 2)^2+ 4[/tex]

- #6

PeterO

Homework Helper

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or if you like

-x^{2}+ 4x

= -(x^{2}- 4x)

= -(x^{2}- 4x + 4) + 4

I put in +4 inside the parentheses, but due to the minus sign out front, I have actually added -4, so to balance, I have to add + 4.

= -(x - 2)^{2}+ 4

-x

= -[x

= -[x

= -[(x - 2)

= -(x - 2)

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