Question 607002
(4√5-8√2)(5√5+10√2)=
:
({{{4sqrt(5)-8sqrt(2)}}})*({{{5sqrt(5)+10sqrt(2)}}})
FOIL
First: {{{4sqrt(5)*5sqrt(5)}}} = 20(5) = 100, we have sqrt(5)*sqrt(5) so it's just 5
:
Outer: {{{4sqrt(5)*10sqrt(2)}}} = {{{40sqrt(10)}}}
:
Inner: {{{-8sqrt(2)*5sqrt(5)}}} = {{{-40sqrt(10)}}}
:
Last:  {{{-8sqrt(2)*10sqrt(2)}}} = -80(2) = -160
:
so we have
100 + {{{40sqrt(10)}}} - {{{40sqrt(10)}}} - 160
The middle two terms cancel out, leaving
100 - 160 = -60
:
Did this un-confuse you somewhat?