4x² + 1................................
( 2x - √-1) (2x +√-1) .........................
( 2x - i ) ( 2x + i )...................
i refers to an imaginary number,we used it when cases like √-1 occur... so the factors are "( 2x - i ) and ( 2x + i )" or "[ x+(1/2) i ] and [ x - (1/2) i]"....
