Missing coordinates?

[Toomanysteps]

Hello, I don't know if I'm writing this in the right place because I don't know if this has something to do with algebra because I'm way behind in Math in my class because I moved to another country that doesn't speak my native language. Let me try to translate this with Google translate because my German is really bad which is one of the reasons why I suck at math.

all the points listed belong to the functional graph for Y = 2x + 8. Solve the missing coordinates.

How do I find out the answers? What are the steps? I did some of it at school and a classroom assistant pretty much did the first three questions for me. Look at task two I roughly translated it above btw

 

[Toomanysteps]

I think you should move this to pre-algerba or differental equations. I should've looked at the different sub-forums.

 

[MarkFL]

Hello, and welcome to FMH!

It appears that the function being considered is:

[MATH]y=2x^2+8[/MATH]
So, if we are given the \(x\)-coordinate of a point, we can simply substitute for \(x\) to find \(y\). If we are given the \(y\)-coordinate, then we may solve the above relation for \(x\) to obtain:

[MATH]x=\pm\sqrt{\frac{y-8}{2}}[/MATH]
In the first one (a) we are told the \(x\)-coordinate is 5, and so:

[MATH]y=2(5)^2+8=58[/MATH]
In the third one (c) we are told the \(y\)-coordinate is 0, and so:

[MATH]x=\pm\sqrt{\frac{0-8}{2}}=\pm2i[/MATH]
This is an imaginary value, and so we know there is no point on the graph of the given function having the given \(y\)-coordinate.

Can you do the rest?

 

[Steven G]

Here is another way to see the third one..

x may be negative, positive or 0.

Now when we square a negative or a positive number we get a positive number. When we square 0 we get 0. So x^2 is either 0 or positive no matter what number we use for x. Now if we add 8 to that (to get x^2 + 8), then the value will be 8 or larger. That is y = x^2 + 8 is 8 or larger. So y can not equal 0, which is what is indicated in the 3rd part. So there is no such x!