Solution assignment 03 Quadratic functions and graphs

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Assignment 3

Given the function:

y=x^2-8x+15

Answer the following questions:

  1. What is the intersection point of the graph with the Y-axis?
  2. Does the graph have intersection points with the X-axis, and if so, how many? Calculate the coordinates.
  3. What is the symmetry axis?

Solution

1. Because c in the formula equals 15, the intersection point with the Y-axis equals (0,15).

2. In order to find out whether the graph of the function has intersection points with the X-axis, we have to calculate the discriminant. However, we can also notice that the equation can be factorized:

y=x^2-8x+15=(x-5)(x-3)

Then we kill two birds with one stone. There are two intersection points with the X-axis and their coordinates are (3,0) and (5,0).

3. The symmetry axis lies just in the middle of these two points and thus the symmetry axis is x=4.

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