What is the axis of symmetry for the graph of y – 4x = 7 – x2 ?

  x = 2

Step-by-step explanation:

A graph shows the axis of symmetry easily. It is the x-coordinate of the vertex.

  x = 2

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You can rearrange the equation to ...

  y -7 = 4x -x^2

  y -7 = x(4 -x)

The axis of symmetry is halfway between x-values that give the same y-value. Here, y=7 for x=0 and for x=4. That is, the right side of this equation is zero at those x-values. The axis of symmetry is halfway between, at x = (0+4)/2 = 2

The axis of symmetry is x=2.

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Alternate solutions

In standard form,

  ax^2 +bx +c = y

the axis of symmetry is ...

  x = -b/(2a)

Putting this equation into that form, we have ...

  -x^2 +4x +7 = y

  x = -(4)/(2(-1))

  x = 2 . . . . axis of symmetry

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We can rearrange the equation to vertex form.

  y -7 = -x^2 +4x

  y -7 -4 = -(x^2 -4x +4) . . . . . add the square of half the x-coefficient inside parentheses. Add an equal amount to the other side of the equation.

  y -11 = -(x -2)^2

This tells us the vertex of the graph is (2, 11), so the axis of symmetry is x=2.

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2. Definition of congruent angles

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