Quadratic Formula Problem

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miss.alley

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My teacher wants me to find the x and y intercepts of my problems. But i forgot how to do that with these particular problems. So i need help with the entire thing.
The equation is : f(x)=3x squared - 6x- 9
so far i have only used the quadratic formula for this equation. and came up with x=3, -1. But i am pretty sure that is not what my teacher had intended my answer to be. please help me i am very desperate at this point. thank u. :)
 
miss.alley said:
My teacher wants me to find the x and y intercepts of my problems. But i forgot how to do that with these particular problems. So i need help with the entire thing.
The equation is : f(x)=3x squared - 6x- 9
so far i have only used the quadratic formula for this equation. and came up with x=3, -1. But i am pretty sure that is not what my teacher had intended my answer to be. please help me i am very desperate at this point. thank u. :)
Click to expand...
Please tell us:

What is the definition of x-intercept of a function?

What is the definition of y-intercept of a function?

What do you find when you solve the quadratic equation?
 
ok i now that an x intercept is when the point when the crosses the x-axis
and that the y intercept is when the point crosses the y axis
and using the quadratic formula i got x= 3 and x=-1
 
miss.alley said:
ok i now that an x intercept is when the point when the crosses the x-axis
and that the y intercept is when the point crosses the y axis
and using the quadratic formula i got x= 3 and x=-1
Click to expand...

The answer is CORRECT.

But, the intercept is the point of intersection of the line with axis.
 
miss.alley said:
ok.
then would i be ready to graph this equation?
Click to expand...

It's actually a parabola . . .

Take several points and you will be able to graph it.
 
miss.alley said:
ok i now that an x intercept is when the point when the crosses the x-axis <<< What is/are the value/s of 'y' at these point/s?
and that the y intercept is when the point crosses the y axis<<< What is/are the value/s of 'x' at these point/s?

and using the quadratic formula i got x= 3 and x=-1<<< What are the values of 'y' at these points?
Click to expand...

Your original problem does not ask you to plot the function - at least you did not tell us that in your first post.
 
thats my problem
i do not know how to find the y intercepts at the points that i found (x=3, -1)
 
miss.alley said:
thats my problem
i do not know how to find the y intercepts at the points that i found (x=3, -1)
Click to expand...

Try plugging X=3 and X=-1 back into the original equation. What do you get for y (f(x) is just another way of saying y=)?
When you are using the quadratic formula your answers SHOULD be getting the x intercepts. the x intercept is when you have (#,0) The numbers you are getting when you plug them into the equation and solve for Y should equal 0.

For y intercept set the equation equal to 0 (so put 0 where f(x) is) and solve that is the y-intercept.

Hope I helped.
 


The y-intercept is located somewhere on the y-axis.

Starting at the Origin, you either go straight up or straight down, to get to the y-intercept (depending on its sign).

You never move horizontally (to the left or to the right), so the x-coordinate must be zero.

FACT: All y-intercepts have an x-coordinate of zero because they are always located on the y-axis.

y-intercept coordinates are: (0, y)

y = f(0)

Do you know how to evaluate the number f(0) ? In other words, what is y when x is zero ?

 
LEG7930 said:
For y intercept set the equation equal to 0 (so put 0 where f(x) is) and solve that is the y-intercept.

This is incorrect; your instructions are for finding the x-intercept.

To calculate the y-intercept, set x = 0, and evaluate f(0).

f(0) is the y-coordinate of the y-intercept point.

x is always zero, at any y-intercept, because all y-intercepts are located on the y-axis.
Click to expand...
 
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