Can someone help me with my math analysis homework? =]] Please?

Question

I'm trying to finish my homework so I can just chill over the weekend=]]

Can someone explain to me how to do this... [please...]

Directions: Determine whether the equation represents y as a function of x

13. x^2+y^2=4

15. y=√(x^2-1)

I need: ANYTHING that is helpful=]] like...

explanations

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Thank you so much!

Answer 1

13. not as listed. This can be manipulated to be y as a function of x by solving for y.

y^2=4-x^2

y= sqrt (4 - x^2)

15. y is represented as a function of x