fa' (x) = 3*x^2 - 6a*x + 6*x + 3
3*x^2 - 6a*x + 6*x + 3= 0 | / 3
x^2 - 2a * x + 2 * x + 1 = 0
x^2 + ( 2 - 2a ) *x + 1 = 0 | pq-Forml oder quadr.Ergänzung
x^2 + ( 2 - 2a ) *x + ( 1- a )^2 = -1 +
( 1-a ) ^2
( x + 1 - a ) ^2 = ( 1 - a)^2 - 1
x + 1 - a = ± √ [ ( 1 -a )^2 - 1 ]
x = ± √ [ ( 1 -a )^2 - 1 ] + a -1
oder
x = ± √ ( 1 - 2a + a^2 - 1 ) + a -1
x = ± √ ( a^2 - 2a ) + a -1