How Do You Find the X-Intercepts of a Quadratic Function?

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In summary, the conversation discussed how to sketch the graph of a function using shifts and stretches of the parent function y=x^2. The orientation, vertex, axis of symmetry, y-intercept, point symmetric to the y-intercept, x-intercepts, and maximum or minimum value were all mentioned as important features to consider when completing the graph. The steps of factoring and solving for x-intercepts were also discussed.
  • #1
math4life
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Homework Statement


Sketch the graph of each function given using shifts and stretches of the parent function y=x2 (not by simply plotting points). Clearly indicate and explicitly state the orientation, vertex, axis of symmetry, y-intercept, and point symmetric to the y-intercept, the x-intercepts, and the maximum or minimum value of each function. Use these features to complete your graph.

f(x)=-x2-4x

Homework Equations


The Attempt at a Solution


My factoring(please check):
f(x)=-x2-4x
f(x)=-(x2-4x+4)+4=0
f(x)=-(x-2)2+4=0.
Finding the x intercepts is the part I am stuck on.

The y intercept is obviously 0, so we have 0,0.
I know that the other x intercept will be at 4 due to the similar proportion (I think) but I want to know how to find that.

We get -4=-(x-2)2
+-SQRT(-4)=-x+2
-x=-2+-SQRT(-4)
X=2+-SQRT(-4)

That's a non real answer. Please someone check my math on solving for the x intercept. The rest of the problem I have done.
 
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  • #2
Here's a hint: look very, very, very, closely, at the signs inside parentheses going from the first row to the second in your work (duplicated below)

[tex]
\begin{align*}
f(x) & = -x^2 - 4x \\
f(x) & = - \left(x^2 - 4x + 4\right) + 4 = 0
\end{align*}
[/tex]

Also, to be mathematically correct, you should hold off on the " = 0 " portion until you've finished re-writing [tex] f(x) [/tex]
as you want to. After the re-writing, set the new form equal to zero and solve.
 
  • #3
Got it, thanks! :) Answer my next thread please- lol.
 

FAQ: How Do You Find the X-Intercepts of a Quadratic Function?

What are the x intercepts?

The x intercepts are the points where a graph crosses the x-axis, meaning that the y-coordinate is equal to 0.

How do you find the x intercepts?

To find the x intercepts, set the y-coordinate equal to 0 and solve for the x-value using algebraic methods such as factoring, the quadratic formula, or completing the square.

Why are the x intercepts important?

The x intercepts are important because they give us information about the behavior of a graph. They can tell us about the roots or solutions of a function, the symmetry of the graph, and the behavior of the graph near the x-axis.

Can there be more than two x intercepts?

Yes, there can be more than two x intercepts on a graph. This can happen with polynomial functions of degree 3 or higher, which can have multiple roots or solutions.

How do you interpret the x intercepts?

The x intercepts can be interpreted as the points where the graph intersects with the x-axis. They can also represent the roots or solutions of a function, which can have real or complex values.

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