Question

16.
Prove the following by constructing t
(i) (p v q) vr + pv (q vr) (​

Answer 1

it is because of the following equivalence law, which you can prove from a truth table:

r→s≡¬r∨s.

If you let r=p∧q and s=p∨q, you get what you are looking for, namely that

(p∧q)→(p∨q)≡¬(p∧q)∨(p∨q).