Question

Tính :

a) \(\left(5+4\sqrt{2}\right)\left(3+2\sqrt{1+\sqrt{2}}\right)\left(3-2\sqrt{1+\sqrt{2}}\right)\)

b) \(\dfrac{3\sqrt{8}-2\sqrt{12}+\sqrt{40}}{3\sqrt{18}-2\sqrt{27}+\sqrt{45}}\)

Answer 1

a) \(\left(5+4\sqrt{2}\right)\left(3+2\sqrt{1+\sqrt{2}}\right)\left(3-2\sqrt{1+\sqrt{2}}\right)\)

= \(\left(5+4\sqrt{2}\right)\left(9-\left(2\sqrt{1+\sqrt{2}}\right)^2\right)\)

= \(\left(5+4\sqrt{2}\right)\left(9-4\left(1+\sqrt{2}\right)\right)\) = \(\left(5+4\sqrt{2}\right)\left(9-4-4\sqrt{2}\right)\)

= \(\left(5+4\sqrt{2}\right)\left(5-4\sqrt{2}\right)\) = \(25-\left(4\sqrt{2}\right)^2\) = \(25-32=-7\)