How to determine abc formula

The general formula : ax2+ bx+ c
a, b, c is real number
a, b equals coefficients
c equals constanta

Then to get the formula:
The general formula: ax2+ bx+ c
1. the equation square divided by a, the formula become : x square plus bx over a plus c over a equals 0
2. then the formula plus square of b over 2a in each part, the formula become : x square plus bx over a plus square of b over 2a plus c over a equals square of b over 2a
3. the formula become : square of x plus b over 2a equals b square over 4a square minus c over a
equals b square minus 4ac all over 4a square
4. then the formula become : x plus b over 2a equals ± square root of b square minus 4ac all over 4a square
5. the formula become : x equals minus b over 2a plus square root of b square minus 4ac all over 4a square, or
x equals plus b over 2a plus square root of b square minus 4ac all over 4a square.