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In these exercises, determine whether the equation represents y as a function of x.


19. \(y=\sqrt{x^2-1}\)

21. 2x+3y=4

23. y2=x2-1


I believe 19 and 23 are the same thing, am I correct or incorrect in said assumption?

 Sep 11, 2017

19.  y  = sqrt ( x^2 - 1)


This is the top half of a hyperbola


See the graph, here....https://www.desmos.com/calculator/cop6acsqup


Notice that this passes the vertical line test.. each x value is only associated with one y value...so it is a function


21.  2x + 3y  = 4   


This is the equation of a [nonvertical] line......this will always be a function


23 . y^2 = x^2 - 1


This graph is similar to 19, but is the complete hyperbola.....it does not pass the vertical line test because two different y's are associated with the same x value......[for instance.....if x = 2, y takes on the values  sqrt (2)  and - sqrt (2) ]


See the graph, here :  https://www.desmos.com/calculator/g13bkuiecg


Notice that the vertical line x = 2 cuts the graph in two places....



cool cool cool

 Sep 11, 2017

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