Determine the Intersection Points of y = (x - 9)(x + 7) with the X-Axis

Finding X-Intercepts with Factored Quadratics

Determine the points of intersection of the function

y=(x9)(x+7) y=(x-9)(x+7)

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
00:14 Find what zeroes each factor in the product
00:21 This is one solution
00:29 This is the second solution
00:38 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=(x9)(x+7) y=(x-9)(x+7)

With the X

2

Step-by-step solution

To solve this problem, we'll determine where the function intersects the x-axis by following these steps:

  • Step 1: Set the function equal to zero to find the roots.
  • Step 2: Solve each factor of the equation independently for x x .
  • Step 3: Confirm the intersection points as the solutions.

Now, let's work through each step:
Step 1: Given the function y=(x9)(x+7) y = (x-9)(x+7) , set y=0 y = 0 to find the x-intercepts:
(x9)(x+7)=0 (x-9)(x+7) = 0 .

Step 2: Solve the equation:
The expression (x9)(x+7)=0(x-9)(x+7) = 0 implies that either x9=0x-9 = 0 or x+7=0x+7 = 0.

Solving each equation:
For x9=0x-9 = 0, solve for xx:
x=9x = 9.
For x+7=0x+7 = 0, solve for xx:
x=7x = -7.

Step 3: Therefore, the points of intersection are where y=0y = 0, which occur at:

The solutions are x=9x = 9 and x=7x = -7.

The coordinates of these intersection points, given y=0y = 0 at each root, are (7,0)(-7, 0) and (9,0)(9, 0).

Therefore, the solution to the problem is (7,0),(9,0)(-7, 0), (9, 0).

3

Final Answer

(7,0),(9,0) (-7,0),(9,0)

Key Points to Remember

Essential concepts to master this topic
  • Rule: Set function equal to zero to find x-intercepts
  • Technique: Use zero product property: if (x-9)(x+7) = 0, then x = 9 or x = -7
  • Check: Substitute back: (9-9)(9+7) = 0(16) = 0 and (-7-9)(-7+7) = (-16)(0) = 0 ✓

Common Mistakes

Avoid these frequent errors
  • Confusing x-intercepts with y-intercepts
    Don't set x = 0 to find x-intercepts = gives you the y-intercept (0, -63) instead! X-intercepts occur where the graph crosses the x-axis, so y = 0. Always set the entire function equal to zero to find x-intercepts.

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?

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

What is the zero product property?

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If two numbers multiply to give zero, then at least one of them must be zero. So if (x9)(x+7)=0 (x-9)(x+7) = 0 , then either x9=0 x-9 = 0 or x+7=0 x+7 = 0 .

Do I need to expand the factored form first?

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No! The factored form (x9)(x+7) (x-9)(x+7) is actually easier to work with. You can immediately apply the zero product property without expanding.

How do I write the final answer?

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X-intercepts are coordinate points on the x-axis. Since y = 0 at these points, write them as (7,0) (-7, 0) and (9,0) (9, 0) , not just the x-values.

What if the function wasn't already factored?

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You'd need to factor the quadratic first (if possible) or use other methods like the quadratic formula. The factored form makes finding x-intercepts much easier!

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