a*b*(c+d)+2*a*b*c+3*d*a*b= abc+abd+2abc+3abd=3abc+4abd
b*(a+c)+2*c(a+b)=ba+bc+2ac+2cb=ab+3bc+2ac
(c+a)*c+3*c²-a*c =c²+ac+3c²-ac=4c²
a*b*(c+d)+2*a*b*c+3*d*a*b= abc+abd+2abc+3abd=3abc+4abd
b*(a+c)+2*c(a+b)=ba+bc+2ac+2cb=ab+3bc+2ac
(c+a)*c+3*c²-a*c =c²+ac+3c²-ac=4c²