then reload this page.
Question 2. Slide the values of $a$, $h$, and $k$, and find an equation in the form
$y=a(x-h)^2+k$ that matches the data.
[Hint: Use the location of the vertex to find $h$ and $k$.
Use the direction that the parabola opens to guess the value of $a$. The error to
the right of the grid will be 0.0 (and it will disappear) when your parabola matches the data.]
Question 3. Click inside the grid to the left and drag the mouse to the left or right.
To the right of the grid you will see the x and $y$-values of the point on
the graph with the $x$-value you have selected.
You can also use the left and right arrow keys to move in small increments.
Example: Find an equation for the parabola without using the sliders.
Now all that is left to do is find the value of $a$. To do this, pick a point on the
graph, say $(0,0.4)$. Because this point is on the graph, you can substitute 0 for
$x$ and 0.4 for $y$ in $y=a(x-2)^2+20$:
So, an equation for the parabola is: $y=-4.9(x-2)^2+20$
Question 4. The main cables of the Golden Gate Bridge have the shape of part of a
parabola. Each tower of the Golden Gate Bridge rises 152m above the roadbed. The length of the
main span is 1280m. We wish to find an equation for a parabola that could model the Golden
Gate's main cables. The diagram below shows a graph of the main cables of the Golden Gate
Bridge. The vertex of the parabola is assumed to be at the origin.
Use the sliders to find an equation in the form $y=a(x-h)^2+k$
that approximates the main cables of the Golden Gate Bridge to within about 0.5 meters.
Question 6. Use the method shown in the example below question 3 to find an equation
for the main cables of the Golden Gate Bridge. (You can use a calculator to do the
One of the most important discoveries in science was the description of how gravity affects
objects rising from or falling to the earth's surface. In 1638 Galileo claimed that the height
of such an object is a quadratic function of its time in the air.
Question 7. Suppose that a baseball player hits the ball straight above home plate. If
the bat meets the ball 0.49 meters above the ground and sends it up at a rate of 30.42 meters
per second, then the height of the ball, in meters, $t$ seconds later is predicted by the
Click inside the grid to the left and drag the mouse to the left or right. On the right hand
side of the grid you can see the $t$ and $h$ values of the point you
have selected. Use the graph and the equation to answer the following questions.
What do you think an equation for the height of the ball would be if the bat gave it a
vertical velocity of 27 meters per second?
Question 9. A bakery sells more loaves of bread when it reduces its price, but if the
price is too low, then the profits are very low. The function
models the bakery's daily profits in dollars, where $x$ is the price of a loaf of bread in
dollars. To the left is a graph of this function.