Question 114770
find the domain 
y=sqrt 4-x^2
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The radicand cannot be negative:
4-x^2>=0
x^2-4<=0
(x-2)(x+2)<=0
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Mark x=-2 and x=+2 on a number line.
Check test values in each of the resulting x-intervals to see where the
solution intervals lie.
Test: 
x=-3 ; 9-4<=0 ; false
x=0: 0-4<=0; true
x=3; 9-4<=0; false
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Solution interval: (-2,2)
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Cheers,
Stan H.