(√5-а)(√5+а) (b+√с)(4√с-b) (√z-√7)(√z+√7) (√2m+√11n)(√11n-√2m)
(-a))=5-2a+ (√z-√7)=z-2√7z+7 (√2m-√11n)=2m-2√22mn+11n