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A parabola is defined by the equation f(x) = (x−4)2 − 9. Find the turning point E, the x-intercept A (with the smaller x-value), the y-intercept C, and the reflection M of C in the axis of symmetry. T

Mathematics

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6 parts
4.1
(4, -9)
4.2
(1, 0)
4.3
(8, 7)
4.4

y=−74x+7y = -\frac{7}{4}x + 7

4.5

y=−47x+4y = -\frac{4}{7}x + 4

4.6

x≤0 or 1≤x≤7x \le 0 \text{ or } 1 \le x \le 7

4.1
The equation of the parabola is f(x)=(x−4)2−9f(x) = (x-4)^2 - 9.
This is in the form y=a(x−p)2+qy = a(x-p)^2 + q, where (p,q)(p, q) is the turning point.
Comparing the given equation, the turning point E is (4,−9)(4, -9).
The coordinates of E are (4,−9)\boxed{(4, -9)}.

4.2
A is an x-intercept of f(x)f(x). To find the x-intercepts, set f(x)=0f(x) = 0.

(x−4)2−9=0(x-4)^2 - 9 = 0 (x−4)2=9(x-4)^2 = 9

Take the square root of both sides:

x−4=±9x-4 = \pm\sqrt{9} x−4=±3x-4 = \pm 3

Solve for xx:

x−4=3  ⟹  x=7x-4 = 3 \implies x = 7 x−4=−3  ⟹  x=1x-4 = -3 \implies x = 1

From the graph, A is the x-intercept with the smaller x-value.
The coordinates of A are (1,0)\boxed{(1, 0)}.

4.3
First, find the coordinates of C. C is the y-intercept of f(x)f(x). Set x=0x=0.

f(0)=(0−4)2−9f(0) = (0-4)^2 - 9 f(0)=(−4)2−9f(0) = (-4)^2 - 9 f(0)=16−9f(0) = 16 - 9 f(0)=7f(0) = 7

So, C is (0,7)(0, 7).
The axis of symmetry of f(x)=(x−4)2−9f(x) = (x-4)^2 - 9 is the vertical line x=4x=4 (the x-coordinate of the turning point).
M is the reflection of C(0,7)(0, 7) in the line x=4x=4.
The x-coordinate of C is 0. The distance from C to the axis of symmetry (x=4x=4) is 4−0=44-0=4 units.
The x-coordinate of M will be 4+4=84+4=8.
The y-coordinate remains the same during reflection across a vertical line.
The coordinates of M are (8,7)\boxed{(8, 7)}.

4.4
The equation of line gg is in the form y=mx+cy = mx+c.
C is the y-intercept of ff and gg. From 4.3, C is (0,7)(0, 7). So, c=7c=7.
The equation of gg is y=mx+7y = mx+7.
D is the x-intercept of gg.
DE is parallel to the y-axis, which means D and E have the same x-coordinate.
From 4.1, E is (4,−9)(4, -9). So, the x-coordinate of D is 4.
Since D is an x-intercept, its y-coordinate is 0.
So, D is (4,0)(4, 0).
Now, calculate the gradient mm using points C(0,7)(0, 7) and D(4,0)(4, 0):

m=y2−y1x2−x1=0−74−0=−74m = \frac{y_2 - y_1}{x_2 - x_1} = \frac{0 - 7}{4 - 0} = \frac{-7}{4}

The equation of gg is y=−74x+7\boxed{y = -\frac{7}{4}x + 7}.

4.5
To find the inverse function g−1g^{-1}, swap xx and yy in the equation for gg and solve for yy.
The equation of gg is y=−74x+7y = -\frac{7}{4}x + 7.
Swap xx and yy:

x=−74y+7x = -\frac{7}{4}y + 7

Subtract 7 from both sides:

x−7=−74yx - 7 = -\frac{7}{4}y

Multiply by −47-\frac{4}{7}:

−47(x−7)=y-\frac{4}{7}(x - 7) = y y=−47x+(−47)(−7)y = -\frac{4}{7}x + \left(-\frac{4}{7}\right)(-7) y=−47x+4y = -\frac{4}{7}x + 4

The equation of g−1g^{-1} is y=−47x+4\boxed{y = -\frac{4}{7}x + 4}.

4.6
We need to find the values of xx for which x(f(x))≤0x(f(x)) \le 0.
This inequality holds true if:

  1. x≥0x \ge 0 AND f(x)≤0f(x) \le 0
  2. x≤0x \le 0 AND f(x)≥0f(x) \ge 0

From 4.2, the x-intercepts of f(x)f(x) are x=1x=1 (point A) and x=7x=7 (point B).
Since f(x)f(x) is an upward-opening parabola, f(x)≤0f(x) \le 0 when xx is between or equal to the x-intercepts.
So, f(x)≤0f(x) \le 0 for 1≤x≤71 \le x \le 7.
And f(x)≥0f(x) \ge 0 for x≤1x \le 1 or x≥7x \ge 7.

Now, let's apply these to the two cases:

Case 1: x≥0x \ge 0 AND f(x)≤0f(x) \le 0
This means x∈[0,∞)x \in [0, \infty) AND x∈[1,7]x \in [1, 7].
The intersection of these two conditions is 1≤x≤71 \le x \le 7.

Case 2: x≤0x \le 0 AND f(x)≥0f(x) \ge 0
This means x∈(−∞,0]x \in (-\infty, 0] AND (x∈(−∞,1]x \in (-\infty, 1] or x∈[7,∞)x \in [7, \infty)).
The intersection of these two conditions is x≤0x \le 0.

Combining the results from Case 1 and Case 2, the values of xx for which x(f(x))≤0x(f(x)) \le 0 are:
x≤0 or 1≤x≤7\boxed{x \le 0 \text{ or } 1 \le x \le 7}.

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