Big Ideas Math Algebra 2, 2014
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Big Ideas Math Algebra 2, 2014 View details
2. Characteristics of Quadratic Functions
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Exercise 5 Page 58

Practice makes perfect
a For a quadratic function f(x)=ax^2+bx+c, the y-coordinate of the vertex is the minimum value of the function when a>0.
Let's identify the values of a, b, and c in the given quadratic function. f(x)=4x^2+16x-3 ⇕ f(x)= 4x^2+ 16x+( - 3)

We can see above that a= 4, b= 16, and c= - 3. We will now use these values to find the desired information.

Minimum Value

Since a= 4 is greater than 0, the parabola will open upwards. This means it will have a minimum value, which is given by f ( - b2a ). Before we find the value of the function at this point, we need to substitute a= 4 and b= 16 in - b2a.
- b/2a
â–Ľ
Substitute values and evaluate
- 16/2( 4)
- 16/8
- 2
Now we have to calculate f(- 2). To do so, we will substitute - 2 for x in the given function.
f(x)=4x^2+16x-3
f(- 2)=4(- 2)^2+16(- 2)-3
â–Ľ
Simplify right-hand side
f(- 2)=4(4)+16(- 2)-3
f(- 2)=16-32-3
f(- 2)=- 19
This tells us that the minimum value of the function is - 19.

Domain and Range

Unless there are any specified restrictions on the x-values, the domain of a quadratic function is all real numbers. Therefore, the domain of this function is all real numbers. Furthermore, since a= 4 is greater than 0, the range is all values greater than or equal to the minimum value, - 19. Domain:& All real numbers Range:& y ≥ - 19

Decreasing and Increasing Intervals

Since a= 4 is greater than 0, the function decreases to the left of the minimum value and increases to the right of the minimum value, which we know occurs at x=- 2. Decreasing Interval:& To the left of - 2 Increasing Interval:& To the right of - 2

b For the quadratic function h(x)=ax^2+bx+c, the y-coordinate of the vertex is the maximum value of the function when a<0.
Let's identify the values of a, b, and c in the given quadratic function. h(x)=- x^2+5x+9 ⇕ h(x)= - 1x^2+ 5x+ 9

We can see above that a= - 1, b= 5, and c= 9. We will now use these values to find the desired information.

Maximum Value

Since a= - 1 is less than 0, the parabola will open downwards. This means it will have a maximum value, which is given by h ( - b2a ). Before we find the value of the function at this point, we need to substitute a= - 1 and b= 5 in - b2a.
- b/2a
â–Ľ
Substitute values and evaluate
- 5/2( - 1)
- 5/- 2
5/2
Now we have to calculate h( 52 ). To do so, we will substitute 52 for x in the given function.
h(x)=- x^2 +5x+9
h(5/2)=- (5/2)^2+5(5/2)+9
â–Ľ
Simplify right-hand side
h(5/2)=- 25/4+5(5/2)+9
h(5/2)=- 25/4+25/2+9
h(5/2)=- 25/4+50/4+9
h(5/2)=- 25/4+50/4+36/4
h(5/2)=61/4
This tells us that the maximum value of the function is 614.

Domain and Range

Unless there are any specified restrictions on the x-values, the domain of a quadratic function is all real numbers. Therefore, the domain of this function is all real numbers. Furthermore, since a= - 1 is less than 0, the range is all values less than or equal to the maximum value, 614. Domain:& All real numbers Range:& y ≤ 61/4

Decreasing and Increasing Intervals

Since a= - 1 is less than 0, the function increases to the left of the maximum value and decreases to the right of the maximum value, which we know occurs at 52. Increasing Interval:& To the left of 52 Decreasing Interval:& To the right of 52