Lesson 17
Changing the Vertex
- Let’s write new quadratic equations in vertex form to produce certain graphs.
Problem 1
Here the graph of quadratic function f.
Andre uses the expression (x-5)^2+7 to define f.
Noah uses the expression (x+5)^2-7 to define f.
Do you agree with either of them? Explain your reasoning.
Problem 2
Here are the graphs of y=x^2, y=x^2-5, and y=(x+2)^2-8.
- How do the 3 graphs compare?
- Compare the graphs of y=x^2 and y = x^2-5. What role does the -5 play in the comparison?
- Compare the graphs of y=x^2 and y=(x+2)^2-8. What role does the +2 play in the comparison?
Problem 3
Which equation represents the graph of y=x^2+2x-3 moved 3 units to the left?
y=x^2+2x-6
y=(x+3)^2+2x-3
y=(x+3)^2+2(x+3)
y=(x+3)^2+2(x+3)-3
Problem 4
Select all the equations with a graph whose vertex has both a positive x- and a positive y-coordinate.
y=x^2
y=(x-1)^2
y=(x-3)^2+2
y=2(x-4)^2-5
y=0.5(x+2)^2+6
y=\text-(x-4)^2+3
y=\text-2(x-3)^2+1
Problem 5
The height in feet of a soccer ball is modeled by the equation g(t)=2+50t-16t^2 , where time t is measured in seconds after it was kicked.
- How far above the ground was the ball when kicked?
- What was the initial upward velocity of the ball?
- Why is the coefficient of the squared term negative?
Problem 6
- What is the vertex of the graph of the function f defined by f(x)=\text-(x-3)^2+6?
- Identify the y-intercept and one other point on the graph of this function.
- Sketch the graph of f.
Problem 7
At 6:00 a.m., Lin began hiking. At noon, she had hiked 12 miles. At 4:00 p.m., Lin finished hiking with a total trip of 26 miles.
During which time interval was Lin hiking faster? Explain how you know.
Problem 8
Kiran bought a smoothie every day for a week. Smoothies cost $3 each. The amount of money he spends, in dollars, is a function of the number of days of buying smoothies.
- Sketch a graph of this function. Be sure to label the axes.
- Describe the domain and range of this function.
Problem 9
A deposit of $500 has been made in an interest-bearing account. No withdrawals or other deposits (aside from earned interest) are made for 5 years.
Write an expression to represent the account balance for each of the following situations.
- 6.5% annual interest calculated monthly
- 6.5% annual interest calculated every two months
- 6.5% annual interest calculated quarterly
- 6.5% annual interest calculated semi-annually
Problem 10
Technology required. Function h is defined by h(x) = 5x+7 and function k is defined by k(x) = (1.005)^x.
- Complete the table with values of h(x) and k(x). When necessary, round to 2 decimal places.
- Which function do you think eventually grows faster? Explain your reasoning.
- Use graphing technology to verify your answer to the previous question.
x | h(x) | k(x) |
---|---|---|
1 | ||
10 | ||
50 | ||
100 |