Question

The function f(t) = t2 + 6t − 20 represents a parabola.

Answer 1

The correct answers are:

Question 1 - Part A: f(t)=(t+3)²-29; Part B: (-3, -29), minimum; Question 2 - Part A: H(1) = 124, g(1) = 76.8; H(2) = 166, g(2) = 125.6; H(3) = 176, g(3) = 174.4; H(4) = 154, g(4) = 223.2; Part B: Between 3 and 4 seconds, because that is where the values of g(t) catch up with H(t).

Explanation:

Our quadratic function is in the form f(x)=ax²+bx+c. Our value of a is 1, b is 6, and c is -20.

To write a quadratic in vertex form, first take half of the b value and square it: (6/2)² = 3² = 9. This is what we will add and subtract to the function:

f(t) = t²+6t+9-20-9

The squared portion will be (t+b/2)²:

f(t) = (t+3)²-20-9

f(t) = (t+3)²-29

Vertex form is f(x) = a(x-h)²+k, where (h, k) is the vertex; in our function, (h, k) is (-3, -29).

Since the value of a was a positive, this parabola opens upward; this makes the vertex a minimum.

For Question 2 Part A, substitute the values 1, 2, 3 and 4 in H(t) and g(t).

For Part B, we can see that the values of g(t) are much less than that of H(t) until 3 seconds. From there, we can see that g(t) passes H(t). This means that the solution point, where they intersect, is between 3 and 4 seconds.

Answer 2

Part A: f(t) = t² + 6t - 20
              u = t² + 6t - 20
         + 20            + 20
      u + 20 = t² + 6t
u + 20 + 9 = t² + 6t + 9
      u + 29 = t² + 3t + 3t + 9
      u + 29 = t(t) + t(3) + 3(t) + 3(3)
      u + 29 = t(t + 3) + 3(t + 3)
      u + 29 = (t + 3)(t + 3)
      u + 29 = (t + 3)²
          - 29       - 29
              u = (t + 3)² - 29

Part B: The vertex is (-3, -29). The graph shows that it is a minimum because it shows that there is a positive sign before the x²-term, making the parabola open up and has a minimum vertex of (-3, -29).
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Part A: g(t) = 48.8t + 28           h(t) = -16t² + 90t + 50
            | t |   g(t)  |                          |  t  |  h(t)  |
            |-4|-167.2|                          | -4 | -566 |
            |-3|-118.4|                          | -3 | -364 |
            |-2| -69.6 |                          | -2 | -194 |
            |-1| -20.8 |                          | -1 |  -56  |
            |0 |   -28  |                          |  0  |   50  |
            |1 |  76.8 |                          |  1  |  124 |
            |2 | 125.6|                          |  2  | 166  |
            |3 | 174.4|                          |  3  | 176  |
            |4 | 223.2|                          |  4  | 154  |
The two seconds that the solution of g(t) and h(t) is located is between -1 and 4 seconds because it shows that they have two solutions, making it between -1 and 4 seconds.

Part B: The solution from Part A means that you have to find two solutions in order to know where the solutions of the two functions are located at.