11. Descompuneti in factori :
a) x^2-6x-27 e)x^2+x-2 i)x^2-x-2
b)x^2-4x-5 f)x^2+x-6 j)x^2+4x-12
c)x^2-4x-21 g)x^2+2x-8 k)x^2-2x-3
d)x^2+2x-3 h)x^2-2x-15 L)x^2-x-20