\( \Large \sqrt{28-6\sqrt{3}} = \sqrt{3} a + b \) => \( \Large \sqrt{ \left(1\right)^{2} + \left(3\sqrt{3}\right)^{2} - 6\sqrt{3} } = \sqrt{3}a + b \) => \( \Large \sqrt{ \left(1 - 3\sqrt{3}\right)^{2} } = \sqrt{3}a + b \) => \( \Large \left(1 - 3\sqrt{3}\right) = \sqrt{3}a + b \) On comparing, we get \( \Large a = -3, b =1 \) Therefore, a + b = -3 + 1 = 2
