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B∈{x∈Z/4x+23/2x+1∈Z}

Răspuns :

4x+23/2x+1 se amplifica cu 2x-1⇒(4x+23)(2x-1)/4x²-1 ⇒8x²-4x+46x-23/4x²-1 ⇔8x²+42x-23/4x²-1 ⇔4x²-1=0⇔4x²=1⇔x²=1/4 ⇔x=+-1/2   8x²+42x-23=0Δ=42²+4·8·23 ( calculezi delta si alfi x1 , x2 din formula x1=-42-√Δ/16 si x2=-42+√Δ / 16 )