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Here are a few recommended readings before getting started with this lesson.
Functions are usually named after the algebraic expression that defines them.
Example function | Type of expression | Name of the function |
---|---|---|
y=7 | Constant | Constant function |
y=3x−2 | Linear | Linear function |
y=-x2−2x+1 | Quadratic | Quadratic function |
The same holds true to those functions whose function rule is a radical expression.
A radical function is a function in which the independent variable is in the radicand of a radical expression or has a rational exponent.
Variable in a Radicand | Variable with a Rational Exponent |
---|---|
y=x | y=x21 |
y=3x+1 | y=(x+1)31 |
y=243x+1−4 | y=2(3x+1)41−4 |
Recall that a root with an even index and a negative radicand is not a real number. Therefore, if the index of the radical is even, then the radicand must be non-negative. By following the same reasoning, if the denominator of the rational exponent is even, then the base of the power must be non-negative. The domain of a radical function can be determined with this information.
A radical function in which the index of the radical is 2 is also called a square root function. The parent function of the square root function family is f(x)=x.
Because the square root of a negative number is not a real number, the radicand in a square root function must be non-negative. Therefore, the domain of f(x)=x can be defined as all real numbers greater than or equal to 0. The square root of a non-negative number is also non-negative, which leads to the range of this function being all real numbers greater than or equal to 0.
x | 246−3x+5 | y |
---|---|---|
-2 | 246−3(-2)+5 | ≈8.72 |
-1 | 246−3(-1)+5 | ≈8.46 |
0 | 246−3(0)+5 | ≈8.13 |
1 | 246−3(1)+5 | ≈7.63 |
2 | 246−3(2)+5 | 5 |
Next, the points obtained in the table can be plotted on a coordinate plane and connected with a smooth curve.
The graph shows that the minimum value for y is 5. Also, y tends to infinity as x tends to negative infinity. Therefore, the range of the function is the set of all real numbers greater than or equal to 5.This information can be summarized in a table.
y=anbx+c+d, when n is even | |
---|---|
Sign of a | Range |
Positive (a>0) |
y≥d |
Negative (a<0) |
y≤d |
Domain: x≥0
Range: y≥0
Graph:
x-intercept: x=0
y-intercept: y=0
End Behavior: yx→0 ⟶ 0 and yx→+∞ ⟶+∞
The radicand of a square root must be non-negative.
x | 212x | y |
---|---|---|
0 | 212(0) | 0 |
1 | 212(1) | ≈0.71 |
2 | 212(2) | 1 |
3 | 212(3) | ≈1.22 |
4 | 212(4) | ≈1.41 |
Next, the obtained points can be plotted and connected with a smooth curve.
From the graph, it is seen that the x-intercept and the y-intercept both occur at the origin. It can also be seen that this function increases over its entire domain and that y tends to infinity as x tends to infinity. With this information, the desired characteristics can be written. Recall that the domain and range are both all non-negative real numbers!
Domain | x≥0 |
---|---|
Range | y≥0 |
x-intercept | x=0 |
y-intercept | y=0 |
End Behavior | yx→0 ⟶ 0 and yx→+∞ ⟶+∞ |
A radical function in which the index of the radical is 3 is also called a cube root function. The parent function of the cube root function family is f(x)=3x.
It is worth noting that the cube root is defined for all real numbers. This means that the domain of f(x)=3x is the set of all real numbers. Furthermore, any real number can be written as the cube root of a number. This leads to the range of this function being all real numbers.
x | 53x+1−2 | y |
---|---|---|
-3 | 53(-3)+1−2 | ≈-3.52 |
-2 | 53(-2)+1−2 | ≈-3.38 |
-1 | 53(-1)+1−2 | ≈-3.15 |
0 | 53(0)+1−2 | -1 |
1 | 53(1)+1−2 | ≈-0.68 |
2 | 53(2)+1−2 | ≈-0.52 |
3 | 53(3)+1−2 | ≈-0.42 |
The obtained points can now be plotted and connected with a smooth curve.
The graph shows that y tends to infinity as x tends to infinity and that y tends to negative infinity as x tends to negative infinity. Therefore, the range of the function is the set of all real numbers.
Domain: All real numbers
Range: All real numbers
Graph:
x-intercept: x=-1
y-intercept: y=1
End Behavior: yx→-∞ ⟶ -∞ and yx→+∞ ⟶+∞
The radicand of a cube root can be any real number.
The radicand of a cube root can be any real number. Therefore, the domain of the function is the set of all real numbers. To determine the range, intercepts, and end behavior, the function will be first drawn on a coordinate plane. To do so, a make a table of values using both positive and negative values!
x | 3x+1 | y |
---|---|---|
-4 | 3-4+1 | ≈-1.44 |
-3 | 3-3+1 | ≈-1.26 |
-2 | 3-2+1 | -1 |
-1 | 3-1+1 | 0 |
0 | 30+1 | 1 |
1 | 31+1 | ≈1.26 |
2 | 32+1 | ≈1.44 |
3 | 33+1 | ≈1.59 |
4 | 34+1 | ≈1.71 |
Next, the calculated points can be plotted and connected with a smooth curve.
The graph suggests that the range is the set of all real numbers. It shows that the x-intercept occurs at x=-1 and the y-intercept at y=1. It can also be seen that y tends to negative infinity as x tends to negative infinity, and that y tends to infinity as x tends to infinity. With this information, the desired characteristics can be written.
Domain | All real numbers |
---|---|
Range | All real numbers |
x-intercept | x=-1 |
y-intercept | y=1 |
End Behavior | yx→-∞ ⟶ -∞ and yx→+∞ ⟶+∞ |
Find the domain and the range of the given radical function.
It is worth noting that radical inequalities in two variables can be graphed the same way as any other inequality in two variables.
x | 32x−4+3 | y |
---|---|---|
-4 | 32(-4)−4+3 | ≈0.71 |
-3 | 32(-3)−4+3 | ≈0.85 |
-2 | 32(-2)−4+3 | 1 |
-1 | 32(-1)−4+3 | ≈1.18 |
0 | 32(0)−4+3 | ≈1.41 |
1 | 32(1)−4+3 | ≈1.74 |
2 | 32(2)−4+3 | 3 |
3 | 32(3)−4+3 | ≈4.26 |
4 | 32(4)−4+3 | ≈4.59 |
Plot the points and draw the boundary curve. Since the given inequality is strict, the boundary curve will be dashed.
x=0, y=0
Zero Property of Multiplication
Subtract terms
Use a calculator
The region above the curve should be shaded.
Thanks to his knowledge of radical functions, Vincenzo is continuously improving his performance at football.
When passing the ball, he realized that if the ball is above the path described by a radical function, opposing players are not able to intercept it. All in all, Vincenzo wants his passes to satisfy the following radical inequality.A radical inequality can be graphed by drawing the boundary curve, testing a point, and shading the corresponding region.
x | 33x−6−1 | y |
---|---|---|
-3 | 33(-3)−6−1 | ≈-3.47 |
-2 | 33(-2)−6−1 | ≈-3.29 |
-1 | 33(-1)−6−1 | ≈-3.08 |
0 | 33(0)−6−1 | ≈2.82 |
1 | 33(1)−6−1 | ≈-2.44 |
2 | 33(2)−6−1 | -1 |
3 | 33(3)−6−1 | ≈0.44 |
4 | 33(4)−6−1 | ≈0.82 |
5 | 33(5)−6−1 | ≈1.08 |
Next, the points obtained in the table can be plotted and connected with a smooth curve. Because the given inequality is a strict inequality, the curve will be dashed.
Now the correct region must be shaded. To determine which region to shade, a point not on the boundary curve will be tested. The point (0,0) seems like the easiest choice.x=0, y=0
Identity Property of Addition
Zero Property of Multiplication
Subtract term
Calculate root
Vincenzo's knowledge about radical functions and inequalities led his team to the regional finals!
For the final game, Vincenzo realized that if the ball is thrown along or above the curve of a square root function, his passes will never be intercepted by an opponent. This means that his team can win the regional championship and qualify for state! Consider the following inequality.To graph the inequality, start by drawing the boundary curve. Then, test a point not on the curve and shade the corresponding region.
x | 221x−1+1 | y |
---|---|---|
2 | 221(2)−1+1 | 1 |
3 | 221(3)−1+1 | ≈2.41 |
5 | 221(5)−1+1 | ≈3.45 |
10 | 221(10)−1+1 | 5 |
The points can be plotted and connected with a smooth curve. Remember that since the inequality is not strict, the curve will be solid.
Finally, the correct region should be shaded. To determine which region to shade, a point not on the curve must be tested. The point (10,3) looks like a good choice. This point will be evaluated in the given inequality. The test point does not satisfy the inequality. Therefore, the region that does not contain this point should be shaded. Keep in mind that the domain of the related function is the set of real numbers greater than or equal to 2. Therefore, to shade the region, only the x-values greater than 2 must be considered.The difference in the domain of each type of function is reflected in its graph.
As already stated, the domain of this type of function is the set of all real numbers that makes the radicand non-negative. This means that the corresponding graph does not extend from negative infinity to positive infinity on the horizontal axis. The graph instead starts at a certain x-value.