Решение задания 1

a) $$\sqrt{x^2 - 18y + 9y^2} = \sqrt{(x-9y)^2}= |x-9y|$$

б) $$(\sqrt{(x + 6y)(x – 6y)})^2 = (\sqrt{x^2 - 36y^2})^2 = x^2 - 36y^2$$

в) $$5a(\sqrt{121 – x})(\sqrt{121 + x}) = 5a\sqrt{(121-x)(121+x)}=5a\sqrt{121^2 - x^2} = 5a\sqrt{14641-x^2}$$