(4√2+2√5) (4√2-2√5) bagai mana cara perkalian bentuk akar

(4√2+2√5)(4√2-2√5)
<=> (4√2)^2-(4√2)(2√5)+(2√5)(4√2)-(2√5)^2
<=> (4x4x2)-(4x2√2x5)+(2x4√5x2)-(2x2x5)
<=> 32-8√10+8√10-20
<=> 32-20
<=> 12