Find the Intersection Points: Solve the Quadratic y=(4x+8)(x+1)

Quadratic x-intercepts with Factored Form

Determine the points of intersection of the function

y=(4x+8)(x+1) y=(4x+8)(x+1)

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 points with the X-axis, the Y value must = 0
00:07 Substitute Y = 0 and solve to find X values
00:13 Find what makes each factor in the product zero
00:18 This is one solution
00:39 This is the second solution
00:45 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=(4x+8)(x+1) y=(4x+8)(x+1)

With the X

2

Step-by-step solution

To solve this problem, we'll follow these steps:

  • Step 1: Set the function y=(4x+8)(x+1) y = (4x + 8)(x + 1) equal to zero, i.e., (4x+8)(x+1)=0 (4x + 8)(x + 1) = 0 .
  • Step 2: Apply the zero-product property to resulting factors.
  • Step 3: Solve each equation for x x .

Now, let's work through each step:
Step 1: We start by setting the equation to zero:
(4x+8)(x+1)=0(4x + 8)(x + 1) = 0.

Step 2: Using the zero-product property, we find:
1. 4x+8=04x + 8 = 0
2. x+1=0x + 1 = 0

Step 3: Solve each of these equations for x x :

For 4x+8=04x + 8 = 0, subtract 8 from both sides to get 4x=84x = -8. Divide both sides by 4, resulting in:
x=2x = -2.

For x+1=0x + 1 = 0, subtract 1 from both sides to get:
x=1x = -1.

Thus, the points of intersection of the function with the x-axis are the solutions we just found. At these points, the y-value is zero, giving us the intersection points as (1,0)(-1, 0) and (2,0)(-2, 0).

Therefore, the solution to the problem is (1,0),(2,0)(-1, 0), (-2, 0).

3

Final Answer

(1,0),(2,0) (-1,0),(-2,0)

Key Points to Remember

Essential concepts to master this topic
  • Zero Product Property: If ab = 0, then a = 0 or b = 0
  • Technique: Set each factor equal to zero: 4x + 8 = 0 gives x = -2
  • Check: Substitute back: (4(-2)+8)(-2+1) = (0)(-1) = 0 ✓

Common Mistakes

Avoid these frequent errors
  • Setting y equal to zero instead of the entire function
    Don't set just y = 0 and ignore the function = you're missing the equation! This gives no useful information about x-values. Always set the entire function equal to zero: (4x+8)(x+1) = 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 do we set the function equal to zero to find x-intercepts?

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X-intercepts are points where the graph crosses the x-axis. At these points, the y-coordinate is always zero. So we set y = 0 to find where the function equals zero!

What if the function wasn't already factored?

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You'd need to factor the quadratic first before using the zero product property. Expand (4x+8)(x+1) (4x+8)(x+1) to get 4x2+12x+8 4x^2 + 12x + 8 , then factor it back.

Why are the intersection points written as (x, 0) instead of just x-values?

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Intersection points are coordinates with both x and y values. Since we're finding x-intercepts, the y-coordinate is always 0, giving us points like (-1, 0) and (-2, 0).

Can I solve this by expanding and using the quadratic formula instead?

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Yes, but it's much harder! Since the function is already factored, using the zero product property is the fastest method. Save the quadratic formula for when factoring is difficult.

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

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Solve each factor separately: 4x+8=0 4x + 8 = 0 gives x=2 x = -2 , and x+1=0 x + 1 = 0 gives x=1 x = -1 . Both are equally valid solutions!

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