\(a\left(b-c\right)-b\left(a+c\right)=\left(a+b\right).\left(-c\right)\)
\(a.b-a.c+b.a-b.c=\left(a+b\right).\left(-c\right)\)
\(a.\left(b-b\right)+\left(a+b\right).\left(-c\right)=\left(a+b\right).\left(-c\right)\)
\(a.0+\left(a+b\right).\left(-c\right)=\left(a+b\right).\left(-c\right)\)
\(\left(a+b\right).\left(-c\right)=\left(a+b\right).\left(-c\right)\)
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