a) ab+ac=
=a(b+c)=
= -4×(-15)=60
b) ab-ac=
=a(b-c)=
= -11×(-12)=132
a = -4
b + c = -15
ab + ac =
dam factor comun pe a
a·(b + c) =
-4 · (-15) =
60
a = - 11
b-c = -12
ab-ac =
a·(b-c) =
-11 · (-12) =
132
