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Sa se arate ca pt orice n ∈ N numarul este irational: √105n+12 (totul este sub radical)

Răspuns :

presupunem ca √(105n +12) ∈ Q

caz 1) n-par =>n=2k

√(105n+12)= √(....0)+12=  √(......2) ∈Q (fals)

caz 2)n-impar  =>n=2k+1

√(105n+12)=  √(....5)+12=  √(......7) ∈Q  (fals)
presupunem ca √(105n +12) ∈ Q

caz 1) n-par =>n=2k

√(105n+12)= √(....0)+12=  √(......2) ∈Q (fals)

caz 2)n-impar  =>n=2k+1