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Problem 11 - Entrance Test

If log₂(x-1) + log₂(x+3) = 4, then x equals

Correct: C

Combine: log₂[(x-1)(x+3)]=4 → (x-1)(x+3)=16 → x²+2x-19=0 → x=(-2±√80)/2=-1±2√5. Only x=1+2√5≈5.47, closest integer 5.