I assume you mean the mixed number 1 + 7/9.
As an improper fraction, we have
1 7/9 = 1 + 7/9 = 9/9 + 7/9 = (9 + 7)/9 = 16/9
Then the square root of this is
√(1 7/9) = √(16/9) = √(4²/3²) = √((4/3)²) = 4/3
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