Question 1209028
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I'll provide 3 hints


Hint #1
{{{drawing(400,400,-8,7,-5,10,
graph(400,400,-8,7,-5,10,-1000),
circle(0,0,4),circle(0,4,4)
)}}}
The lower and upper circles have centers (0,0) and (0,4) respectively.
Both circles have radius 4.


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Hint #2
The equations of the lower and upper circles are {{{x^2+y^2=16}}} and {{{x^2+(y-4)^2=16}}} in that order.


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Hint #3
{{{x^2+y^2=16}}} rearranges to {{{x^2=16-y^2}}}


Plug this into {{{x^2+(y-4)^2=16}}} and you'll get {{{16-y^2+(y-4)^2=16}}}
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