Determine the X-axis Intersection Points of the Quadratic Function: y = (x-1)(2x+1)

Finding X-Intercepts with Factored Quadratics

Determine the points of intersection of the function

y=(x1)(2x+1) y=(x-1)(2x+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 point with the X-axis, the Y value must = 0
00:07 Set Y = 0 and solve to find X values
00:13 Find what zeroes each factor in the multiplication
00:32 This is one solution
00:57 This is the second solution
01:10 Let's verify that each solution truly zeroes the Y value
01:36 This solution zeroes
01:50 Let's check the second solution
02:15 This solution also zeroes, these are the intersection points with the X-axis
02:24 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=(x1)(2x+1) y=(x-1)(2x+1)

With the X

2

Step-by-step solution

To find the points of intersection with the x-axis for the function y=(x1)(2x+1) y = (x-1)(2x+1) , we must determine when y=0 y = 0 .

Using the zero-product property, set each factor equal to zero separately:

  • x1=0 x - 1 = 0
  • 2x+1=0 2x + 1 = 0

Solving the first equation, x1=0 x - 1 = 0 :
Add 1 to both sides:
x=1 x = 1 .

Solving the second equation, 2x+1=0 2x + 1 = 0 :
Subtract 1 from both sides:
2x=1 2x = -1 .
Divide both sides by 2:
x=12 x = -\frac{1}{2} .

The solutions are the x-intercepts of the function. Therefore, the points of intersection are (1,0) (1, 0) and (12,0) \left(-\frac{1}{2}, 0\right) .

Thus, the points of intersection on the x-axis are (12,0)(- \frac{1}{2}, 0) and (1,0)(1, 0).

3

Final Answer

(12,0),(1,0) (-\frac{1}{2},0),(1,0)

Key Points to Remember

Essential concepts to master this topic
  • Zero Product Property: If ab = 0, then a = 0 or b = 0
  • Set Each Factor to Zero: x - 1 = 0 gives x = 1; 2x + 1 = 0 gives x = -1/2
  • Verify X-Intercepts: Both points have y-coordinate of 0 on the x-axis ✓

Common Mistakes

Avoid these frequent errors
  • Setting y equal to each factor instead of zero
    Don't set y = x - 1 and y = 2x + 1 separately = gives wrong coordinates! This finds where factors equal y, not where the function crosses the x-axis. Always set the entire function y = (x-1)(2x+1) equal to zero first.

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 I 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, meaning the y-coordinate is always 0. So you're looking for values of x where y = 0.

What if the quadratic isn't already factored?

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You'll need to factor it first! Look for two numbers that multiply to give the constant term and add to give the middle coefficient, or use the quadratic formula.

Can a quadratic have more than two x-intercepts?

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No! A quadratic function can have at most 2 x-intercepts. It might have exactly 2 (like this problem), exactly 1, or none at all.

How do I write the final answer as coordinate points?

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X-intercepts are always written as (x-value, 0). Since they're on the x-axis, the y-coordinate is always zero. So x=1 x = 1 becomes (1,0) (1, 0) .

What does the zero product property actually mean?

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It means that if you multiply two or more numbers and get zero, at least one of those numbers must be zero. It's impossible to multiply non-zero numbers and get zero!

Should I expand the factored form first?

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No! Keep it factored - that's the whole advantage! Expanding (x1)(2x+1) (x-1)(2x+1) to 2x2x1 2x^2 - x - 1 just makes the problem harder.

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