Square root of 1

Two correct Answers : +1 (plus one) and -1 (minus one).

Logic :
Square of +1 = (+1 * +1) = +1 = 1 ; Implies +1 is square root of 1
Square of -1 = (-1 * -1) = +1 = 1 ; Implies -1 is square root of 1

Labels : square root -1, irrational number, irrational, infinite, the square root of -1

Mathematics book deals

Square root of -1
Answer : i (for imaginary unit) defined square root of -1. Studied in complex number theory.