Question

елси не вы то мне училка Пашей даст​

Answer 1

$1)\ \ \sqrt{54}+\sqrt{24}-\sqrt6=\sqrt{6\cdot 9}+\sqrt{6\cdot 4}-\sqrt6=3\sqrt6+2\sqrt6-\sqrt6=4\sqrt6\\\\\\2)\ \ (\sqrt{x}-2)(\sqrt{x}+2)-2(x-2)=(x-4)-2x+4=-x\\\\\\3)\ \ \dfrac{5a}{\sqrt5-1}=\dfrac{5a\cdot (\sqrt5+1)}{(\sqrt5-1)(\sqrt5+1)}=\dfrac{5a\cdot (\sqrt5+1)}{5-1}=\dfrac{5a\cdot (\sqrt5+1)}{4}=\dfrac{5\sqrt5\, a+5a}{4}$

Answer 2

$\sqrt{54} + \sqrt{24} - \sqrt{6} = \sqrt{3 {}^{2} \times 6 } + \sqrt{2 {}^{2} \times 6} - \sqrt{6} = 3 \sqrt{6} + 2 \sqrt{6} - \sqrt{6} = 5 \sqrt{6} - \sqrt{6} = 4 \sqrt{6}$

$( \sqrt{x} - 2)( \sqrt{x} + 2) - 2(x - 2) = ( \sqrt{x} ) {}^{2} - {2}^{2} - 2(x - 2) = x - 4 - 2x + 4 = - x$

$\frac{5a}{ \sqrt{5} - 1 } = \frac{5a \times ( \sqrt{5} + 1) }{ (\sqrt{5} - 1 )( \sqrt{5} + 1) } = \frac{5 \sqrt{5} a+ 5a }{( \sqrt{5} ) {}^{2} - 1 } = \frac{5 \sqrt{5} a + 5a}{5 - 1} = \frac{5 \sqrt{5} a + 5a}{4}$