Lesson 7
Rewriting Quadratic Expressions in Factored Form (Part 2)
- Let’s write some more expressions in factored form.
Problem 1
Find two numbers that...
- multiply to -40 and add to -6.
- multiply to -40 and add to 6.
- multiply to -36 and add to 9.
- multiply to -36 and add to -5.
If you get stuck, try listing all the factors of the first number.
Problem 2
Create a diagram to show that \((x-5)(x+8)\) is equivalent to \(x^2+3x-40\).
Problem 3
Write a \(+\) or a \(-\) sign in each box so the expressions on each side of the equal sign are equivalent.
- \((x \; \boxed{\phantom{30}} \;18)(x \; \boxed{\phantom{30}} \; 3)=x^2-15x-54\)
- \((x \; \boxed{\phantom{30}} \; 18)(x \; \boxed{\phantom{30}} \; 3)=x^2+21x+54\)
- \((x \; \boxed{\phantom{30}} \; 18)(x \; \boxed{\phantom{30}} \; 3)=x^2+15x-54\)
- \((x \; \boxed{\phantom{30}} \; 18)(x \; \boxed{\phantom{30}} \; 3)=x^2-21x+54\)
Problem 4
Match each quadratic expression in standard form with its equivalent expression in factored form.
Problem 5
Rewrite each expression in factored form. If you get stuck, try drawing a diagram.
- \(x^2 -3x-28\)
- \(x^2 +3x-28\)
- \(x^2 +12x-28\)
- \(x^2 -28x-60\)
Problem 6
Which equation has exactly one solution?
\(x^2=\text-4\)
\((x+5)^2=0\)
\((x+5)(x-5)=0\)
\((x+5)^2=36\)
Problem 7
The graph represents the height of a passenger car on a ferris wheel, in feet, as a function of time, in seconds since the ride starts.
Use the graph to help you:
- Find \(H(0)\).
- Does \(H(t)=0\) have a solution? Explain how you know.
- Describe the domain of the function.
- Describe the range of the function.
Problem 8
Elena solves the equation \(x^2=7x\) by dividing both sides by \(x\) to get \(x=7\). She says the solution is 7.
Lin solves the equation \(x^2=7x\) by rewriting the equation to get \(x^2-7x=0\). When she graphs the equation \(y=x^2-7x\), the \(x\)-intercepts are \((0,0)\) and \((7,0)\). She says the solutions are 0 and 7.
Do you agree with either of them? Explain or show how you know.
Problem 9
A bacteria population, \(p\), can be represented by the equation \(p = 100,\!000 \boldcdot \left(\frac{1}{4} \right)^d\), where \(d\) is the number of days since it was measured.
- What was the population 3 days before it was measured? Explain how you know.
- What is the last day when the population was more than 1,000,000? Explain how you know.