Descompuneti in produs de factori ireductibili urmatoarele expresii :
a) x^2 -9x+14
b)x^2 -6x -16
c) 4x^2 - (x-1)^2
d)x^3 +2x^2 -9x -18
e) 5x+15+xy + 3y
F) x^2 +11x+28