Lets 5 = a

square root 5 = b

then (a+b)(a-B) =

a2 - b2 =

(5)2 – (square root of 5)2 =

25-5 = 20

square root 5 = b

then (a+b)(a-B) =

a2 - b2 =

(5)2 – (square root of 5)2 =

25-5 = 20