a) x^2+2x-x-2=x(x-1)+2(x-1)=
=(x-1)(x+2)
b) x^2+4x-3x-12=x(x+4)-3(x+4)=(x+4)(x-3)
c) x^2-3x+2x-6=x(x-3)+2(x-3)=
=(x-3)(x+2)
d) x^2-5x+4x-20=x(x-5)+4(x-5)=(x-5)(x+4)
e) x^2-7x+5x-35=x(x-7)+5(x-7)
=(x-7)(x+5)
f) x^2-4x+x-4=x(x-4)+(x-4)=
=(x-4)(x+1)
g) x^2+7x-2x-14=x(x+7)-2(x+7)
=(x+7)(x-2)
h) x^2-7x+3x-21=x(x-7)+3(x-7)=
=(x-7)(x+3)