a^4 - 10 a^3 + 22 a^2 + 12 a= a ( a^4 - 10 a^3 + 22 a^2 + 12 a )= a ( a - 6 ) ( a^2 - 4 a - 2 )= a ( a - 6 ) [ ( a - 2 )^2 - 6 ]= a ( a - 6 ) ( a - 2 - √6 ) ( a - 2 + √6 )