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A quadratic function has x-intercepts 2 and 6 and its vertex is (4, 8). What is the corresponding quadratic expression? A. 2x2 − 16x + 24 B. -2x2 + 16x – 24 C. -2x2 - 16x + 24 D. -x2 − 16x + 12 E. -x2 − 16x – 24

Sagot :

Given:

A quadratic function has x-intercepts 2 and 6 and its vertex is (4, 8).

To find:

The corresponding quadratic expression.

Solution:

If graph of a function intersect the x-axis at c, then (x-c) is a factor of the function.

A quadratic function has x-intercepts 2 and 6. It means (x-2) and (x-6) are two factors of the required quadratic function.

The function is defined as:

[tex]P(x)=a(x-2)(x-6)[/tex]                    ...(i)

Where, a is a constant.

The vertex of the quadratic function is (4,8). It means the point (4,8) will satisfy the function.

Substituting x=4 and P(x)=8 in (i).

[tex]8=a(4-2)(4-6)[/tex]

[tex]8=a(2)(-2)[/tex]

[tex]8=-4a[/tex]

Divide both sides by -4.

[tex]\dfrac{8}{-4}=a[/tex]

[tex]-2=a[/tex]

Putting [tex]a=-2[/tex] in (i), we get

[tex]P(x)=-2(x-2)(x-6)[/tex]

[tex]P(x)=-2(x^2-6x-2x+12)[/tex]

[tex]P(x)=-2(x^2-8x+12)[/tex]

[tex]P(x)=-2x^2+16x-24[/tex]

Therefore, the correct option is B.