Problem: Quadratic identities

Problem

Prove that \(\left( a+b \right)\left( c+d \right)=ac+ad+bc+bd\) using the distributive law \(a\left( b+c \right)=ab+ac\) . Hint: let \(e=a+b\) . Then \(\left( a+b \right)\left( c+d \right)=e(c+d)\) . Now use the distributive law.. several times.