Solve Quadratic Equation x^2 - 9 for X-Axis Intersections

Quadratic Functions with Factored Form Intercepts

Determine the points of intersection of the function

y=(x+3)(x3) y=(x+3)(x-3)

With the X

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Find the intersection point with X-axis
00:03 At the intersection point with X-axis, Y value must = 0
00:07 Substitute Y = 0 and solve for X values
00:14 Find what makes each factor zero in the product
00:20 This is one solution
00:28 This is the second solution
00:35 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Determine the points of intersection of the function

y=(x+3)(x3) y=(x+3)(x-3)

With the X

2

Step-by-step solution

To determine the points of intersection of the function y=(x+3)(x3) y = (x+3)(x-3) with the x-axis, we need to find the x-values where y=0 y = 0 . These are called the x-intercepts.

We begin by setting the function equal to zero:

(x+3)(x3)=0 (x+3)(x-3) = 0

Using the zero-product property, if a product of two terms is zero, then at least one of the factors must be zero. Thus, we set each factor equal to zero and solve for x x :

  • First factor: x+3=0 x + 3 = 0
    • Solving for x x , we subtract 3 from both sides:
      x=3 x = -3
  • Second factor: x3=0 x - 3 = 0
    • Solving for x x , we add 3 to both sides:
      x=3 x = 3

Hence, the solutions for x x where y=0 y = 0 are x=3 x = -3 and x=3 x = 3 .

Therefore, the points of intersection of the function with the x-axis are (3,0) (-3, 0) and (3,0) (3, 0) .

Comparing with the given answer choices, the correct choice is (3,0),(3,0) (3,0),(-3,0) .

Therefore, the points of intersection are (3,0),(3,0) (3,0),(-3,0) .

3

Final Answer

(3,0),(3,0) (3,0),(-3,0)

Key Points to Remember

Essential concepts to master this topic
  • X-Intercepts: Set function equal to zero and solve for x-values
  • Zero-Product Property: If (x+3)(x3)=0 (x+3)(x-3) = 0 then x = -3 or x = 3
  • Check: Substitute back: (3+3)(33)=0(6)=0 (-3+3)(-3-3) = 0 \cdot (-6) = 0

Common Mistakes

Avoid these frequent errors
  • Using y-coordinates other than zero for x-intercepts
    Don't write intercepts as (3,3) or (-3,-3) = wrong coordinates! X-intercepts are where the graph crosses the x-axis, so y must always be zero. Always write x-intercepts as (x-value, 0).

Practice Quiz

Test your knowledge with interactive questions

The following function has been graphed below:

\( f(x)=-x^2+5x+6 \)

Calculate points A and B.

BBBAAACCC

FAQ

Everything you need to know about this question

Why are x-intercepts always written with y = 0?

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X-intercepts are points where the graph crosses the x-axis. Since the x-axis is where y = 0, all x-intercepts have coordinates (x-value, 0).

What's the difference between x-intercepts and y-intercepts?

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X-intercepts: Set y = 0 and solve for x (where graph crosses x-axis)
Y-intercepts: Set x = 0 and solve for y (where graph crosses y-axis)

Can I expand the factored form first?

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You could expand (x+3)(x3) (x+3)(x-3) to get x29 x^2 - 9 , but it's easier to use the zero-product property directly on the factored form!

What if one of my factors doesn't equal zero?

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Both factors must be checked! The zero-product property says at least one factor equals zero. Each factor that equals zero gives you an x-intercept.

How do I know which answer choice is correct?

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Look for the choice with both x-intercepts as (x-value, 0). In this problem, both (-3, 0) and (3, 0) should be listed, regardless of order.

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