Question

21 и 22 и объясните ответ

Answer 1

21)
$sqrt{a} + sqrt{a + 2} = 3 \ sqrt{a} - sqrt{a + 2} = frac{( sqrt{a} - sqrt{a + 2})( sqrt{a} + sqrt{a + 2}) }{ sqrt{a} + sqrt{a + 2} } = frac{ {( sqrt{a}) }^{2} - {( sqrt{a + 2} )}^{2} }{ sqrt{a} + sqrt{a + 2} } = frac{a - (a + 2)}{3} = frac{a - a - 2}{3} = - frac{2}{3}$
22)
$sqrt{a} - sqrt{a + 5} = - 3 \ sqrt{a} + sqrt{a + 5} = frac{( sqrt{a} + sqrt{a + 5})( sqrt{a} - sqrt{a + 5} )}{ sqrt{a} - sqrt{a + 5} } = frac{ {( sqrt{a} )}^{2} - {( sqrt{a + 5} )}^{2} }{ sqrt{a} - sqrt{a + 5} } = frac{a - (a + 5)}{ - 3} = frac{a - a - 5}{ - 3} = frac{5}{3}$