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The vertex is on the axis of symmetry.
A
The vertex is on the axis of symmetry. Let's recall the formula for the axis of symmetry using the coefficients of a quadratic in standard form.
| Option | Equation | x-coordinate of the Vertex | |
|---|---|---|---|
| Expression | Value | ||
| A | y= 1x^2 -8x+ 15 | --8/2( 1) | 4 |
| B | y= -1x^2 -4x+ 12 | --4/2( -1) | -2 |
| C | y= 1x^2+ 6x+ 8 | -6/2( 1) | -3 |
| D | y= -1x^2 -2x+ 2 | --2/2( -1) | -1 |
In three options, the sign of a and b is the same, so the x-coordinate of the vertex is negative. For f(x)=x^2-8x+15 the x-coordinate of the vertex is 4. The correct answer is A.