Pearson Algebra 2 Common Core, 2011
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Pearson Algebra 2 Common Core, 2011 View details
3. Rational Functions and Their Graphs
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Exercise 16 Page 521

Division by zero is not defined. This means that the denominator cannot be zero.

Domain: All real numbers except x=2 and x=3
Points of Discontinuity: Removable at x=2, and non-removable at x=3
x-intercepts: None
y-intercept: (0,1)

Practice makes perfect

We want to find the domain, points of discontinuity, and x- and y-intercepts of the graph of the given rational function. We also want to determine whether the discontinuities are removable or non-removable. Let's do these things one at a time.

Domain

Consider the given function. y=6-3x/x^2-5x+6 To find the domain, we will start by factoring the denominator.
y=6-3x/x^2-5x+6
y=6-3x/x^2-2x-3x+6
â–Ľ
Factor out x & - 3
y=6-3x/x(x-2)-3x+6
y=6-3x/x(x-2)-3(x-2)
y=6-3x/(x-2)(x-3)
We have fully factored the denominator.

y=6-3x/(x- 2)(x- 3) Recall that division by zero is not defined. Therefore, the rational function is undefined where x- 2=0 and where x- 3=0. ccc x- 2=0 & and & x- 3=0 ⇕ & & ⇕ x= 2 & and & x= 3 This means that neither x= 2 nor x= 3 are included in the domain. Domain All real numbers except x= 2 and x= 3

Points of Discontinuity

If a real number a is not in the domain of a function, then the function has a point of discontinuity at x=a. Since the domain is all real numbers except x= 2 and x= 3, we can write the points of discontinuity of our function. Points of Discontinuity x= 2 and x= 3 To determine whether the discontinuities are removable or non-removable, we will factor the numerator and cancel out any common factors between the numerator and denominator.
y=6-3x/(x-2)(x-3)
y=- 3(- 2+x)/(x-2)(x-3)
y=- 3(x-2)/(x-2)(x-3)
y=- 3/x-3
Now that we have simplified the equation, let's consider the points of discontinuity, x= 2 and x= 3.
  • The factor x- 2 is not in the denominator any more, so x= 2 is a removable point of discontinuity.
  • The factor x- 3 is still in the denominator, so x= 3 is a non-removable point of discontinuity.

Intercepts

The intercepts of a function are the points where the graph intersects the axes. Let's calculate the intercepts of the given function, if there are any.

x-intercepts

The x-intercepts of a function are the points where the graph intersects the x-axis. At these points, the value of the y-coordinate is zero. Therefore, to find the x-intercepts, we have to substitute 0 for y in the function rule and solve for x.
y=6-3x/x^2-5x+6
0=6-3x/x^2-5x+6
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Solve for x
0=6-3x
3x=6
x=2
We found that if y=0, the value of x is 2. However, x=2 is not included in the domain of the function. Therefore, there are no x-intercepts.

y-intercept

The y-intercept of a function is the point where the graph intersects the y-axis. At this point, the value of the x-coordinate is zero. Therefore, to find the y-intercept, we have to substitute 0 for x in the function rule and solve for y.
y=6-3x/x^2-5x+6
y=6-3( 0)/0^2-5( 0)+6
â–Ľ
Simplify right-hand side
y=6-0/0-0+6
y=6/6
y=1
The y-intercept of the graph is the point (0,1).