Help! Can you check my answer?

Question

anonymous · Answer

I think its the second graph

anonymous · Answer

I think you're guessing.

loser66 · Answer

x^2+y^2=9 is the equation of a circle--> the second graph is not a correct one

anonymous · Answer

now im really confused :( can someone help me?

loser66 · Answer

@johnweldon1993  help her, please. I am not good at explanation

johnweldon1993 · Answer

Hmm well I guess a good way to go about it would to continue on what you said...

$$\large x^2 + y^2 = r^2$$ is the equation of a circle, where r is the radius (notice not r^2)


So if your equation is

$$\large x^2 + y^2 = 9$$

Comparing that to
$$\large x^2 + y^2 = r^2$$

That means the radius of the circle would be $\large \sqrt{9}$ which = $\large 3$

So your graph should have a circle on it, with a radius of 3

johnweldon1993 · Answer

Also (if the whole circle thing is confusing to you at the moment)

the other equation you have is

y = x + 3

We know this to be a straight line with a y-intercept (crossing the y-axis) of 3

There is only 1 graph choice given where the line crosses through the y-axis at 3

anonymous · Answer

thank you so much, i had never seen that equation before, it makes it alot easier :)

johnweldon1993 · Answer

Hmm, I'm very surprised that it was on your question selection then...

Regardless (look it over) but it is always good when you can eliminate other possible answers

Just like I did when we noticed that there is only 1 graph that applies to $\large y = x + 3$ it just worked in our favor that we could eliminate all but the correct answer