Janie

05-30-2006, 02:30 PM

Find the vertex of the parabola

f(x)=3x squared +18x-3

f(x)=3x squared +18x-3

View Full Version : Vertex of the parabola

Janie

05-30-2006, 02:30 PM

Find the vertex of the parabola

f(x)=3x squared +18x-3

f(x)=3x squared +18x-3

tkhunny

05-30-2006, 03:34 PM

Find the vertex of the parabola

f(x)=3x squared +18x-3f(x) = 3(x<sup>2</sup> + 6x - 1)

Can you "Complete the Square" on the part inside the parentheses? That will do it.

f(x)=3x squared +18x-3f(x) = 3(x<sup>2</sup> + 6x - 1)

Can you "Complete the Square" on the part inside the parentheses? That will do it.

Janie

05-30-2006, 03:59 PM

f(x)=3(xsquared+6x-1)

no because I don't know why you put 6x in there

this is very difficult

no because I don't know why you put 6x in there

this is very difficult

tkhunny

05-30-2006, 04:01 PM

I didn't put the '6x' in there.

Let's review the Distributive Property of Multiplication over Addition.

3(x<sup>2</sup> + 6x - 1) = 3x<sup>2</sup> + 18x - 3

Does that ring any bells? If we're stuck on this important, fundamental property, it will be very difficult to move on.

Let's review the Distributive Property of Multiplication over Addition.

3(x<sup>2</sup> + 6x - 1) = 3x<sup>2</sup> + 18x - 3

Does that ring any bells? If we're stuck on this important, fundamental property, it will be very difficult to move on.

Mrspi

05-30-2006, 04:35 PM

Find the vertex of the parabola

f(x)=3x squared +18x-3

For a parabola whose equation is

f(x) = ax<sup>2</sup> + bx + c

the x-coordinate of the vertex is -b/2a. Once you have the x-coordinate, substitute it for x in the equation, and evaluate to find f(x)....which is the y-coordinate of the vertex.

Your equation is

f(x) = 3x<sup>2</sup> + 18x - 3

a = 3, and b = 18. The x-coordinate of the vertex, -b/2a, is -18/2(3), or -18/6, or -3. Now substitute -3 for x:

f(-3) = 3(-3)<sup>2</sup> + 18(-3) - 3

Do the arithmetic on the right-hand side, and you'll have the y-coordinate of the vertex.

I hope this helps you.

f(x)=3x squared +18x-3

For a parabola whose equation is

f(x) = ax<sup>2</sup> + bx + c

the x-coordinate of the vertex is -b/2a. Once you have the x-coordinate, substitute it for x in the equation, and evaluate to find f(x)....which is the y-coordinate of the vertex.

Your equation is

f(x) = 3x<sup>2</sup> + 18x - 3

a = 3, and b = 18. The x-coordinate of the vertex, -b/2a, is -18/2(3), or -18/6, or -3. Now substitute -3 for x:

f(-3) = 3(-3)<sup>2</sup> + 18(-3) - 3

Do the arithmetic on the right-hand side, and you'll have the y-coordinate of the vertex.

I hope this helps you.

Janie

05-30-2006, 04:46 PM

f (-3)=24

do I then divide by -3

if so is it f=-8

do I then divide by -3

if so is it f=-8

skeeter

05-31-2006, 09:59 AM

f (-3)=24

do I then divide by -3

if so is it f=-8

I have no idea what you are doing.

first of all, f(-3) does not equal 24, f(-3) = 3(-3)<sup>2</sup> + 18(-3) - 3 = -30.

second ... are you unfamiliar with function notation?

you do not "divide" by -3 ... the function evaluated at x = -3 is f(-3) = y = -30

the vertex of the parabola is located at (-3,-30).

do I then divide by -3

if so is it f=-8

I have no idea what you are doing.

first of all, f(-3) does not equal 24, f(-3) = 3(-3)<sup>2</sup> + 18(-3) - 3 = -30.

second ... are you unfamiliar with function notation?

you do not "divide" by -3 ... the function evaluated at x = -3 is f(-3) = y = -30

the vertex of the parabola is located at (-3,-30).

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