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1a) Let f(x)=ax^2-4x-c. A horizontal line, L, intersects the graph of f at x= -1 and x=3.

The equation of the axis of symmetry is x=p. Find P

The equation of the axis of symmetry is x=p. Find p

1b) Hence, show that a=2

1c) The equation of L is y=5. Find the value of C.​

Respuesta :

The answer will be c

The equation of the axis of symmetry is [tex]\mathbf{x =1}[/tex], the value of a is 2, and the value of c is 1.

The function is given as:

[tex]\mathbf{f(x) = ax^2 -4x - c}[/tex]

Line L is represented as:

[tex]\mathbf{(x,y) = (-1,5)(3,5)}[/tex]

Substitute the above values in: [tex]\mathbf{f(x) = ax^2 -4x - c}[/tex]

So, we have:

[tex]\mathbf{5 = a(-1)^2 - 4(-1) - c}[/tex]

[tex]\mathbf{5 = a(3)^2 - 4(3) - c}[/tex]

Expand [tex]\mathbf{5 = a(-1)^2 - 4(-1) - c}[/tex]

[tex]\mathbf{5 = a + 4 - c}[/tex]

Expand [tex]\mathbf{5 = a(3)^2 - 4(3) - c}[/tex]

[tex]\mathbf{5 = 9a - 12 - c}[/tex]

Subtract [tex]\mathbf{5 = a + 4 - c}[/tex] and [tex]\mathbf{5 = 9a - 12 - c}[/tex]

[tex]\mathbf{5 - 5 = a - 9a + 4 + 12 -c + c}[/tex]

[tex]\mathbf{0 = - 8a + 16}[/tex]

Collect like terms

[tex]\mathbf{8a = 16}[/tex]

Divide both sides by 8

[tex]\mathbf{a = 2}[/tex]

Substitute [tex]\mathbf{a = 2}[/tex] in [tex]\mathbf{5 = a + 4 - c}[/tex]

[tex]\mathbf{5 = 2 + 4 - c}[/tex]

[tex]\mathbf{5 = 6 - c}[/tex]

Subtract 6 from both sides

[tex]\mathbf{-1 = - c}[/tex]

So, we have:

[tex]\mathbf{c = 1}[/tex]

Recall that:

[tex]\mathbf{f(x) = ax^2 -4x - c}[/tex]

Where:

[tex]\mathbf{a = 2}[/tex] and [tex]\mathbf{b = -4}[/tex]

The equation of the axis of symmetry is:

[tex]\mathbf{x = -\frac{b}{2a}}[/tex]

So, we have:

[tex]\mathbf{x = -\frac{-4}{2 \times 2}}[/tex]

[tex]\mathbf{x = -\frac{-4}{4}}[/tex]

[tex]\mathbf{x =1}[/tex]

Hence, the equation of the axis of symmetry is [tex]\mathbf{x =1}[/tex], the value of a is 2, and the value of c is 1.

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