Полное решение : 3(x+3)²-5(x+3)+2=0

3( x + 3 )² - 5( x + 3 ) + 2 = 0 
3( x² + 6x + 9 ) - 5x - 15 + 2 = 0 
3x² + 18x + 27 - 5x - 13 = 0 
3x² + 13x + 14 = 0 
D = 169 - 168 = 1 = 1²
x1 = ( - 13 + 1 ) : 6 = - 2 
x2 = ( - 13 - 1 ) : 6 = - 14/6 = - 7/3 = - 2 1/3