α = radacina irationala comuna
α² + aα + b = 0
α² + cα + d = 0
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scadem α² +aα + b - α² - cα -d = 0
aα -cα + b -d = 0
α ·( a - c) +( b - d) = 0
scriem 0 ca numar irational 0 = α·0 + 0
α · ( a -c) + ( b -d) = α·0 + 0 daca
α· ( a -c) = α·0 ⇒ a - c = 0 ; a =c
b - d = 0 b = d