Math Problem Statement

In the xy-plane, a parabola has vertex (9, -14) and intersects the x-axis at two points. If the equation of the parabola is written in the form y = ax^2 + bx + c, where a, b, and c are constants, which of the following could be the value of a + b + c ? A) -23 B) -19 C) -14 D) -12

Solution

To find the possible value of a+b+ca + b + c for the parabola with vertex (9,14)(9, -14) that intersects the x-axis at two points, we can start by using the vertex form of a parabola, which is given by:

y=a(xh)2+ky = a(x - h)^2 + k

where (h,k)(h, k) is the vertex. Here, (h,k)=(9,14)(h, k) = (9, -14), so the equation becomes:

y=a(x9)214y = a(x - 9)^2 - 14

To find the x-intercepts (where y=0y = 0), we set the equation to zero:

0=a(x9)2140 = a(x - 9)^2 - 14

This simplifies to:

a(x9)2=14a(x - 9)^2 = 14

Thus, we have:

(x9)2=14a(x - 9)^2 = \frac{14}{a}

For the parabola to intersect the x-axis at two points, 14a\frac{14}{a} must be positive, implying that aa must be positive. Now, taking the square root gives:

x9=±14ax - 9 = \pm \sqrt{\frac{14}{a}}

Thus, the x-intercepts are:

x=9±14ax = 9 \pm \sqrt{\frac{14}{a}}

Now, we can convert the vertex form to standard form y=ax2+bx+cy = ax^2 + bx + c. We expand the vertex form:

y=a(x218x+81)14y = a(x^2 - 18x + 81) - 14

This expands to:

y=ax218ax+(81a14)y = ax^2 - 18ax + (81a - 14)

From this, we identify:

  • b=18ab = -18a
  • c=81a14c = 81a - 14

Now, we can find a+b+ca + b + c:

a+b+c=a18a+(81a14)=(a18a+81a14)=64a14a + b + c = a - 18a + (81a - 14) = (a - 18a + 81a - 14) = 64a - 14

Next, we can analyze the possible values of 64a1464a - 14:

  1. For a=14a = \frac{1}{4}: 64×1414=1614=264 \times \frac{1}{4} - 14 = 16 - 14 = 2

  2. For a=1a = 1: 64×114=6414=5064 \times 1 - 14 = 64 - 14 = 50

  3. For a=12a = \frac{1}{2}: 64×1214=3214=1864 \times \frac{1}{2} - 14 = 32 - 14 = 18

Since we need to determine values of a+b+ca + b + c that could equal one of the options provided:

  • A) -23
  • B) -19
  • C) -14
  • D) -12

To find a+b+ca + b + c equal to these options, we set 64a14=k64a - 14 = k (where kk is one of the options) and solve for aa:

  1. For 23-23: 64a14=23    64a=9    a=964(not possible, as a>0)64a - 14 = -23 \implies 64a = -9 \implies a = -\frac{9}{64} \quad \text{(not possible, as } a > 0\text{)}

  2. For 19-19: 64a14=19    64a=5    a=564(not possible)64a - 14 = -19 \implies 64a = -5 \implies a = -\frac{5}{64} \quad \text{(not possible)}

  3. For 14-14: 64a14=14    64a=0    a=0(not valid)64a - 14 = -14 \implies 64a = 0 \implies a = 0 \quad \text{(not valid)}

  4. For 12-12: 64a14=12    64a=2    a=132(valid, a>0)64a - 14 = -12 \implies 64a = 2 \implies a = \frac{1}{32} \quad \text{(valid, } a > 0\text{)}

Thus, the only valid value is:

12\boxed{-12}

Would you like any further details or explanations on this topic? Here are some questions to consider:

  1. How does the vertex affect the graph of a parabola?
  2. What is the significance of the x-intercepts in a parabola?
  3. Can you derive the equation of a parabola given different sets of points?
  4. How do you determine whether a parabola opens upwards or downwards?
  5. What are the applications of parabolas in real life?

Tip: Always check the sign of aa to determine the direction in which the parabola opens.

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Math Problem Analysis

Mathematical Concepts

Algebra
Quadratic Equations
Vertex Form of Parabolas

Formulas

Vertex form of a parabola: y = a(x - h)^2 + k
Standard form of a parabola: y = ax^2 + bx + c

Theorems

Properties of parabolas
Determining x-intercepts

Suitable Grade Level

Grades 9-12