boolean Definition and 1 Threads

In the part below where the author of this solution, wants to show that: ##a\vee (b\wedge c)=(a\vee b)\wedge (a\vee c)##, in the third equality he adds ##2ac+2ab+2abc=2a\wedge(b\vee c)##; can someone explain to me why can we do this here? Thanks!