Answer
The quadratic function \( y = 12x^2 + 5x - 2 \) has the following features:
- **Axis of Symmetry**: \( x = -\frac{5}{24} \)
- **Vertex (Minimum Point)**: \( \left( -\frac{5}{24}, -\frac{121}{48} \right) \)
- **y-intercept**: \( (0, -2) \)
- **x-intercepts**: \( \left( -\frac{2}{3}, 0 \right) \) and \( \left( \frac{1}{4}, 0 \right) \)
- **Minimum Value**: \( y = -\frac{121}{48} \) at \( x = -\frac{5}{24} \)
When graphed, the parabola opens upward with its lowest point at the vertex. It crosses the y-axis at \( (0, -2) \) and the x-axis at \( \left( -\frac{2}{3}, 0 \right) \) and \( \left( \frac{1}{4}, 0 \right) \).
The graph does not intersect the line \( y = x - 9 \) at any real points.
The discriminant of the quadratic equation \( 12x^2 + 5x - 2 = 0 \) is 121, indicating two distinct real roots.
Solution
We will analyze the quadratic function
y = 12x² + 5x – 2
step‐by‐step, finding its important features and then investigating its intersections with the line y = x – 9. Finally, we will compute its discriminant.
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1. Finding the Axis of Symmetry
For a quadratic in the form y = ax² + bx + c the axis of symmetry is given by
x = –b/(2a).
Here a = 12 and b = 5, so
x = –5/(2·12) = –5/24.
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2. Finding the Turning Point (Vertex)
The x-coordinate of the vertex is the same as the axis of symmetry, x = –5/24. To get the y-coordinate, substitute x = –5/24 into the function:
y = 12(–5/24)² + 5(–5/24) – 2.
Step‑by‑step:
a. Compute (–5/24)²:
(–5/24)² = 25/576.
b. Multiply by 12:
12·(25/576) = 300/576 = 25/48 (since 300/576 reduces dividing numerator and denominator by 12).
c. Compute the second term:
5(–5/24) = –25/24.
It is convenient to use a denominator of 48: –25/24 = –50/48.
d. Express –2 as –96/48.
Combine the terms:
y = (25/48) – (50/48) – (96/48)
= (25 – 50 – 96) / 48
= –121/48.
Thus, the vertex is at
(–5/24, –121/48).
Because a = 12 > 0, the parabola opens upward and the vertex represents a minimum point.
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3. Finding the Intercepts
A. y‑intercept: Set x = 0.
y = 12·0² + 5·0 – 2 = –2.
So, the y‑intercept is (0, –2).
B. x‑intercepts: Solve 12x² + 5x – 2 = 0.
Use the quadratic formula:
x = [ –b ± √(b² – 4ac) ] / (2a).
First, calculate the discriminant for these intercepts:
Δ = 5² – 4·12·(–2) = 25 + 96 = 121.
Then,
x = ( –5 ± √121 ) / (24)
= ( –5 ± 11 ) / 24.
Thus, the two solutions are:
x = (–5 + 11)/24 = 6/24 = 1/4
x = (–5 – 11)/24 = –16/24 = –2/3.
So the x‑intercepts are at (1/4, 0) and (–2/3, 0).
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4. Maximum or Minimum Value
Since the coefficient a = 12 > 0, the parabola opens upward and so the vertex gives the minimum value of the function. The minimum value is y = –121/48 (approximately –2.52) which occurs at x = –5/24.
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5. Sketching the Graph
When sketching the graph, include these features:
• The axis of symmetry: the vertical line x = –5/24.
• The turning point (vertex): (–5/24, –121/48).
• The x‑intercepts: (–2/3, 0) and (1/4, 0).
• The y‑intercept: (0, –2).
• Note that the graph opens upward (minimum at the vertex).
A rough sketch would show a “U‑shaped” parabola with the vertex slightly left of the y‑axis, crossing the x‑axis at x ≈ –0.67 and x ≈ 0.25, and crossing the y‑axis at –2.
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6. Intersection with the Line y = x – 9
To see if the parabola and the line intersect, set their equations equal:
12x² + 5x – 2 = x – 9.
Subtract (x – 9) from both sides:
12x² + 5x – 2 – x + 9 = 0
12x² + 4x + 7 = 0.
Determine the discriminant for this quadratic:
Δ' = (4)² – 4(12)(7) = 16 – 336 = –320.
Since Δ' is negative, there are no real solutions. Therefore, the parabola and the line y = x – 9 do not intersect at any real points.
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7. Discriminant of y = 12x² + 5x – 2
As computed earlier for the x‑intercepts:
Δ = 5² – 4·12·(–2) = 25 + 96 = 121.
A positive discriminant (121 > 0) means the quadratic has two distinct real roots.
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Summary of Answers:
C.1 (Graph y = 12x² + 5x – 2):
• Axis of symmetry: x = –5/24.
• Vertex (turning point): (–5/24, –121/48), which is the minimum point.
• y‑intercept: (0, –2).
• x‑intercepts: (–2/3, 0) and (1/4, 0).
• Minimum value: y = –121/48.
C.12 (Intersection with y = x – 9):
• Setting 12x² + 5x – 2 equal to x – 9 leads to 12x² + 4x + 7 = 0 with a discriminant of –320.
• Therefore, the graph of y = 12x² + 5x – 2 and the line y = x – 9 do not intersect (0 points of intersection).
C.13 (Discriminant of y = 12x² + 5x – 2):
• The discriminant is 121.
This completes the analysis and sketching of the quadratic graph according to the given conditions.
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