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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 |