Math Problem Statement

The path of a toy airplane is modelled by the parabola y = -x^2 + 8x + 1 where x is the horizontal distance in metres and y is the height in metres. a) What is the maximum height of the toy airplane? b) If the height, y, is 8 m, what is the horizontal distance, x, of the toy airplane?

Solution

The problem you uploaded involves a quadratic equation modeling the path of a toy airplane. Let's break down each part:

a) Maximum height of the toy airplane

The equation modeling the path is:

y=x2+8x+1y = -x^2 + 8x + 1

This is a parabola, and since the coefficient of x2x^2 is negative, it opens downwards. The vertex of this parabola will give us the maximum height of the toy airplane.

For any quadratic equation of the form y=ax2+bx+cy = ax^2 + bx + c, the x-coordinate of the vertex can be found using the formula:

x=b2ax = \frac{-b}{2a}

In your equation, a=1a = -1 and b=8b = 8. Let's substitute these values into the formula:

x=82(1)=82=4x = \frac{-8}{2(-1)} = \frac{-8}{-2} = 4

So, the x-coordinate of the vertex is x=4x = 4. To find the maximum height, substitute x=4x = 4 back into the equation for yy:

y=(4)2+8(4)+1=16+32+1=17y = -(4)^2 + 8(4) + 1 = -16 + 32 + 1 = 17

Thus, the maximum height of the toy airplane is 17 meters.


b) Horizontal distance when height is 8 meters

We are given that the height, yy, is 8 meters. To find the corresponding horizontal distances, we substitute y=8y = 8 into the equation:

8=x2+8x+18 = -x^2 + 8x + 1

Rearranging:

0=x2+8x+180 = -x^2 + 8x + 1 - 8 0=x2+8x70 = -x^2 + 8x - 7

Now, we solve this quadratic equation using the quadratic formula:

x=b±b24ac2ax = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}

where a=1a = -1, b=8b = 8, and c=7c = -7. Substituting the values:

x=8±824(1)(7)2(1)x = \frac{-8 \pm \sqrt{8^2 - 4(-1)(-7)}}{2(-1)} x=8±64282x = \frac{-8 \pm \sqrt{64 - 28}}{-2} x=8±362x = \frac{-8 \pm \sqrt{36}}{-2} x=8±62x = \frac{-8 \pm 6}{-2}

This gives two solutions:

  1. x=8+62=22=1x = \frac{-8 + 6}{-2} = \frac{-2}{-2} = 1
  2. x=862=142=7x = \frac{-8 - 6}{-2} = \frac{-14}{-2} = 7

So, the two possible horizontal distances are x=1x = 1 meter and x=7x = 7 meters.


Would you like further clarification or details on any of these steps?

Here are some follow-up questions for you:

  1. What does the negative coefficient of x2x^2 imply about the shape of the parabola?
  2. How would the path change if the coefficient of x2x^2 was positive instead of negative?
  3. What happens to the maximum height if the coefficient bb were increased?
  4. How can we graph this quadratic equation to visually identify the vertex?
  5. If the height were to reach 20 meters, what would the horizontal distance be?

Tip: When working with quadratics, remember the quadratic formula is a powerful tool for finding roots, but you can also factor when the equation is simple enough!

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Math Problem Analysis

Mathematical Concepts

Algebra
Quadratic Equations
Parabolas
Vertex of a Parabola

Formulas

Quadratic equation formula: y = ax^2 + bx + c
Vertex formula: x = -b/(2a)
Quadratic formula: x = [-b ± √(b^2 - 4ac)] / 2a

Theorems

The vertex of a parabola represents the maximum or minimum point.

Suitable Grade Level

Grades 7-9