Not all roles available for this page.
Sign in to view assessments and invite other educators
Sign in using your existing Kendall Hunt account. If you don’t have one, create an educator account.
Which three go together? Why do they go together?
Each row in each table has a pair of equivalent expressions. Complete the tables. If you get stuck, try drawing a diagram.
| factored form | standard form |
|---|---|
| factored form | standard form |
|---|---|
An engineer is designing a fountain that shoots out drops of water. The nozzle from which the water is launched is 3 meters above the ground. It shoots out a drop of water at a vertical velocity of 9 meters per second.
Function models the height in meters, , of a drop of water seconds after it is shot out from the nozzle. The function is defined by the equation .
How many seconds until the drop of water hits the ground?
Here is a clever way to think about quadratic expressions that would make it easier to rewrite them in factored form.
Try the method to write each of these expressions in factored form.
You have probably noticed that the coefficient of the squared term in all of the previous examples is a perfect square. What if that coefficient is not a perfect square?
Here is an example of an expression whose squared term has a coefficient that is not a perfect square.
Use the distributive property to expand . Show your reasoning and write the resulting expression in standard form. Is it equivalent to ?
Try the method to write each of these expressions in factored form.
Only some quadratic equations in the form of can be solved by rewriting the quadratic expression into factored form and using the zero product property. In some cases, finding the right factors of the quadratic expression is quite difficult.
For example, what is the factored form of ?
We could try , or , but will the second number in each factor be -5 and 7, 5 and -7, 35 and -1, or -35 and 1? And in which order?
We have to do some guessing and checking before finding the equivalent expression that would allow us to solve the equation .
Once we find the right factors, we can proceed to solving using the zero product property, as shown here:
What is even trickier is that most quadratic expressions can’t be written in factored form!
Let’s take for example. Can you find two numbers that multiply to make -3 and add up to -4? Nope! At least not easy-to-find rational numbers.
We can use technology to graph the function defined by , which reveals two -intercepts at around and . These give the approximate zeros of the function, -0.646 and 4.646, so they are also approximate solutions to .
The fact that the zeros of this function don’t seem to be simple rational numbers is a clue that it may not be possible to easily rewrite the expression in factored form.
It turns out that rewriting quadratic expressions in factored form and using the zero product property is a very limited tool for solving quadratic equations.
In the next several lessons, we will learn some ways to solve quadratic equations that work for any equation.