Question 227127
y^2 = 7-x^2
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x^2 +y^2 =7
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This  is  a  circle,  center  at  origin,,(0,0),  and  radius sqrt 7
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To  be  a  function,  there  can  be  only  one  value  of  y for  each x value,  not  so  in  this  case.
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The  other  test  for  a  function  is  the  vertical  line  test,,,when  moving  a  vertical  line  along    the  x  axis,  it  should  intersect  only  one  value  of  y,,,,again  not  so  in  this  case
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Therefore,  we  have  a  relationship,  not  a  function.