Quadratic Functions and Zeros

Quadratic Functions Day 2

Tuesday Dec 15, 2020

Multiple Choice

Warm - up: How do you find the zeros of a quadratic function?

• Make one factor equal 0, so the whole thing is 0

• Set each factor equal to zero, and solve for x

• You don't

• What?

Recap from yesterday...

The zeros of a quadratic function are where the function crosses the x-axis (this was called the x-intercept in linear functions)

You find the zeros by setting each factor equal to zero and solving for x

Zeros are written as ordered pairs (x, 0) where x is a number

Multiple Choice

What are the zeros of this function?

$$y\ =\ \left(8x+2\right)\left(x-5\right)$$  

Remember to write fractions in simplest form

• (-2, 8), (-5, 0)

• $$\left(-\frac{2}{8},\ 0\right),\ \left(5,\ 0\right)$$  

• $$\left(-\frac{1}{4},\ 0\right),\ \left(5,\ 0\right)$$  

• There aren't any

Now, let's find the y-intercept

To find the y-intercept, plug in 0 for all the x values and solve

 $y=\left(x-8\right)\left(8x-5\right)$  

 $y=\left(0-8\right)\left(8\left(0\right)-5\right)$  
 $y=\left(-8\right)\left(-5\right)$  
 $y=40$  

y-intercept: (0,40)

Open Ended

Find the y-intercept:

$$y=\left(x-3\right)\left(5x+6\right)$$  

Sometimes you need to factor first

 $y=x^2-2x-24$  

Multiple Choice

Factor:

$$y=x^2-2x-24$$  

• (x + 6)(x - 4)

• (x - 6)(x - 4)

• (x - 6)(x + 4)

• Not factorable

Multiple Choice

What's the y-intercept of

$$y=\left(x-6\right)\left(x+4\right)$$  

• (4, 0)

• (-4, 0)

• (0, 4)

• (0, -4)

Go practice

There's a practice sheet for you in Google Classroom