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a= 1 pe √5-2+1 pe√5+2
aratati ca a apartine(√19;√21)


Răspuns :

1/(√5-2)+1/(√5+2)=(√5+2+√5-2) /(√5+2)(√5-2)=2√5/(5-4)=2√5

2√5=√20
√19<√20<√21
deci A∈(√19 ;√21)