# Textbook algebra graphing help

• May 5th 2009, 03:21 PM
Ryan7123
Textbook algebra graphing help
i have a problem where i have to find the maximum height of a dome with a parabolic curve equation of f(x)= -0.0016xsquared + 75.

the 2nd part is finding the minimum height of the dome if the total length is 250 yards.

• May 5th 2009, 03:47 PM
Jameson
Quote:

Originally Posted by Ryan7123
i have a problem where i have to find the maximum height of a dome with a parabolic curve equation of f(x)= -0.0016xsquared + 75.

the 2nd part is finding the minimum height of the dome if the total length is 250 yards.

Which way does this parabola point? Is it opening up or opening down?

Spoiler:
opening down

Next part:
Spoiler:
So if it opens down the highest point will be the vertex of the parabola. How do you find the vertex?
• May 5th 2009, 04:01 PM
Ryan7123
i have no clue i havent had time to stay for extra help with my teacher this whole concept i have no idea how to do
• May 5th 2009, 04:13 PM
Jameson
Quote:

Originally Posted by Ryan7123
i have no clue i havent had time to stay for extra help with my teacher this whole concept i have no idea how to do

Ok. Well we won't be able to teach you entire chapters in your book. So if you really know nothing about parabolas I suggest you read the section in your book where they are covered.

The standard form for a parabola is $\displaystyle y=ax^2+bx+c$. You can see that your problem is in this form. Since you have a negative number in front of "a", that makes the parabola flip and it goes down. The highest point will be the vertex, which can be found by $\displaystyle x=\frac{-b}{2a}$ in the equation I showed you. That's the x-coordinate.

Does any of this sound familiar or make sense?