Multiply (2�ã7-4�ã2)(4�ã7+8�ã2)
If the non-ascii characters mean
(2√7 - 4√2)(4√7 + 8√2)
then just multiply it out:
2√7*4√7 + 2√7*8√2 - 4√2*4√7 - 4√2*8√2
= 8*7 + 16√14 - 16√14 - 32*2
= 56 - 64
= -8
(2√7 - 4√2)(4√7 + 8√2)
then just multiply it out:
2√7*4√7 + 2√7*8√2 - 4√2*4√7 - 4√2*8√2
= 8*7 + 16√14 - 16√14 - 32*2
= 56 - 64
= -8