Question

What is the equation of the following graph?
Answers:
x2 + y2 = 4

x2 - y2 = 2

x2 + y2 = 2

x2 - y2 = 4

Answer 1

OK, so you have a circle. Do you know what the equation of a circle is and how to graph it? Because that is related to how you do the reverse, find the equation from the graph.

Answer 2

My answer that I came up with is x2 + y2 = 4 or x2 + y2 = 2 @e.mccormick

Answer 3

OK, so you eliminated the - ones because those would not be a circle, which is good. Now, on those two, what would the radius be? That is what is left, finding the radius.

Answer 4

Don't know the radius explain please

Answer 5

Go back to the equation of a circle. What is it? It should be something like \(x^2+y^2=?\) where the question mark is related to the radius.

Answer 6

It's 2 then

Answer 7

x2 + y2 = 2

Answer 8

Well, I wanted it with letters, because it exposes something. Is it 2, or are you missing something on the 2?

Answer 9

No the answer is 2 , x2 + y2 = 2

Answer 10

\(x^2+y^2=r^2\)

Answer 11

ok

Answer 12

If \(x^2+y^2=2\) then \(r^2=2\implies r=\sqrt{2}\). Is that the measure on the picture?

Answer 13

yes

Answer 14

\(\sqrt{2}\approx 1.4142\)

Answer 15

So is the radius in that picture close to one and a half?

Answer 16

No

Answer 17

OK, then lets look at the other...

If \(x^2+y^2=4\) then \(r^2=4\implies r=\sqrt{4}\). Is that the measure on the picture? And what might help is if you look at what \(\sqrt{4}\) is equal to.

Answer 18

it would be 2

Answer 19

right. So if r=2, then the equation becomes:
\(x^2+y^2=2^2\implies x^2+y^2=4\)

Answer 20

Ohhh I see and then you get A

Answer 21

Be careful of the squares! OK? That is one of the mistakes that catches people.

Answer 22

Will do!

Answer 23

Yah, the radius was 2, but the equation was r squared, so 2 squared, so 4. That is one they like to use in homework and tests to get people.