To simplify \( 7\sqrt{99} \), we first simplify \(\sqrt{99}\).
We can factor \(99\) as follows: \[ 99 = 9 \times 11 \] Since \(9\) is a perfect square, we can simplify \(\sqrt{99}\): \[ \sqrt{99} = \sqrt{9 \times 11} = \sqrt{9} \times \sqrt{11} = 3\sqrt{11} \]
Now, substitute back into the expression: \[ 7\sqrt{99} = 7 \times 3\sqrt{11} = 21\sqrt{11} \]
Thus, the simplified form of \( 7\sqrt{99} \) is: \[ \boxed{21\sqrt{11}} \]