Question 82678
Find the domain of f(x)= 7 + sqrt(3x + 21), and express it using interval notation.

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The radicand, 3x+21, cannot negative.
So, you have to determine when it is not negative:
3x+21>=0
3x>=-21
x>=-7
Answer in interval notation: [-7,inf)
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Cheers,
Stan H.