Find the Intersection Points of y = (x-2)(x+4) with the X-Axis

Quadratic Functions with Factored Form

Determine the points of intersection of the function

y=(x2)(x+4) y=(x-2)(x+4)

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 points with the X-axis
00:03 At the intersection with the X-axis, the Y value must = 0
00:07 Substitute Y = 0 and solve for X values
00:13 Find what makes each factor in the product zero
00:18 This is one solution
00:28 This is the second solution
00:32 And this is the solution to the problem

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=(x2)(x+4) y=(x-2)(x+4)

With the X

2

Step-by-step solution

The given problem requires us to find the points where the function y=(x2)(x+4) y = (x-2)(x+4) intersects the x-axis. This is done by determining the values of x x that make y=0 y = 0 .

To find these intersection points:

  • Set the function equal to zero: (x2)(x+4)=0 (x-2)(x+4) = 0 .
  • Apply the Zero Product Property, which states (x2)=0 (x-2) = 0 or (x+4)=0 (x+4) = 0 .
  • Solve each equation:
    • x2=0 x-2 = 0 gives x=2 x = 2 .
    • x+4=0 x+4 = 0 gives x=4 x = -4 .

Thus, the x-coordinates of the intersection points are x=2 x = 2 and x=4 x = -4 . Since these points represent intersections with the x-axis, their corresponding y y -coordinates are 0. This gives us the points:

  • (2,0)(2, 0)
  • (4,0)(-4, 0)

Therefore, the solution to this problem is the points of intersection: (2,0)(2, 0) and (4,0)(-4, 0).

Comparing with the answer choices, the correct choice is:

(2,0),(4,0) (2,0),(-4,0)

3

Final Answer

(2,0),(4,0) (2,0),(-4,0)

Key Points to Remember

Essential concepts to master this topic
  • X-intercepts: Set the function equal to zero to find intersection points
  • Zero Product Property: If (x2)(x+4)=0 (x-2)(x+4) = 0 , then x=2 x = 2 or x=4 x = -4
  • Verify: Check that y=(22)(2+4)=0 y = (2-2)(2+4) = 0 and y=(42)(4+4)=0 y = (-4-2)(-4+4) = 0

Common Mistakes

Avoid these frequent errors
  • Confusing the x-intercepts with the zeros of individual factors
    Don't solve x2=0 x-2 = 0 and think the answer is (2,0) (-2,0) ! This mixes up the sign and gives wrong coordinates. Always solve correctly: x2=0 x-2 = 0 means x=2 x = 2 , giving point (2,0) (2,0) .

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.

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FAQ

Everything you need to know about this question

Why do we set the equation equal to zero?

+

The x-axis is where y=0 y = 0 ! To find where the parabola crosses the x-axis, we need to find all x-values that make the function equal zero.

What if the function wasn't in factored form?

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You'd need to factor the quadratic first or use the quadratic formula. The factored form (x2)(x+4) (x-2)(x+4) makes finding zeros much easier!

How do I remember which factor gives which x-value?

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For (xa)=0 (x-a) = 0 , the solution is x=a x = a . So (x2)=0 (x-2) = 0 gives x=2 x = 2 , and (x+4)=0 (x+4) = 0 gives x=4 x = -4 .

Why are the y-coordinates always 0?

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Because we're finding x-intercepts! These are points where the graph crosses the x-axis, and every point on the x-axis has y=0 y = 0 .

Can I double-check my answer another way?

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Yes! Substitute each x-value back: (22)(2+4)=06=0 (2-2)(2+4) = 0 \cdot 6 = 0 and (42)(4+4)=(6)0=0 (-4-2)(-4+4) = (-6) \cdot 0 = 0 . Both give y=0 y = 0

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