folosim formula ( a -b ) ·( a +b) = a² - b ² , grupata
x = (√2 -1 ) ·( 3 + √5 ) ·(√7 - √6 )· (4 + √7)
y = (√2 +1 )·( 3 - √5 )·( √7 + √6) · ( 4 - √7 )
↓ ↓ ↓ ↓
x·y = ( 2 - 1 ) ·( 9 - 5 ) · ( 7 -6 ) · ( 16 -7 ) = 1 · 4 · 1 · 9 =4·9
med. geom. = √xy = √4·√9 = 2·3 = 6
b . x · y = totul rad . √( 7 -4√3)·(7 +4√3) = rad.( 7² -16·3)= rad.(49 -48 )=
= √1 = 1
med. geom. = √xy = √1 =1