2x2 + 3x + 4 = 0
Move the 4 to the other side: 2x2 + 3x = -4
Divide all terms by 2: x2 + (3/2)x = -2
Complete the square*: x2 + (3/2)x + 9/16 = -2 + 9/16
Factor: (x + 3/4)2 = -23/16
Take the square root: x + 3/4 = +/- sqrt(-23/16)
Subtract 3/4: x = -3/4 +/- sqrt(-23)/4
* You complete the square by dividing the coefficient of the x-term by 2 and squaring the result:
(3/2) / 2 = 3/4 ---> (3/4)2 = 9/16