\(=a\left(ba+b^2+ca-c^2\right)\)\(-bc\left(b+c\right)\)
\(=a\left(a\left(b+c\right)+\left(b+c\right)\left(b-c\right)\right)-bc\left(b+c\right)\)
\(=a\left(b+c\right)\left(a+b-c\right)-bc\left(b+c\right)\)
\(=\left(b+c\right)\left(a^2+ab-ac-bc\right)\)
\(=\left(b+c\right)\left(a-c\right)\left(a+b\right)\)