Răspuns:
26.
[tex]a = \sqrt{9 - \sqrt{56} } = \sqrt{ \frac{9 + \sqrt{81 - 56}}{2} } - \sqrt{ \frac{9 - \sqrt{81 - 56} }{2} } = \sqrt{7} - \sqrt{2} [/tex]
[tex]b = \sqrt{9 + \sqrt{56} } = \sqrt{ \frac{9 + \sqrt{81 - 56} }{2} } + \sqrt{ \frac{9 - \sqrt{81 - 56} }{2} } = \sqrt{7} + \sqrt{2} [/tex]
27.
[tex]x = \sqrt{4 - \sqrt{7} } = \sqrt{ \frac{4 + \sqrt{16 - 7} }{2} } - \sqrt{ \frac{4 - \sqrt{16 - 7} }{2} } = \sqrt{ \frac{7}{2} } - \sqrt{ \frac{1}{2} } = \frac{ \sqrt{14} }{2} - \frac{ \sqrt{2} }{2} = \frac{ \sqrt{2} ( \sqrt{7 - 1)} }{2} [/tex]
[tex]y = \sqrt{4 + \sqrt{7} } = \sqrt{ \frac{4 + \sqrt{16 - 7} }{2} } + \sqrt{ \frac{4 - \sqrt{16 - 7} }{2} } = \sqrt{ \frac{7}{2} } + \sqrt{ \frac{1}{2} } = \frac{ \sqrt{14} }{2} + \frac{ \sqrt{2} }{2} = \frac{ \sqrt{2( \sqrt{7} + 1)} }{2} [/tex]
