by Fawn

(United States)

p(y-3)= yp-3p

After knowing the above, let's see how this can be used to

expand (y+1)(y-3). Now, notice that if we let

p(y-3)=(y+1)(y-3)

Therefore:

Since,p(y-3)= yp-3p

Hence,(y+1)(y-3) =y(y+1)-3(y+1)

From here, we can continue to simplify:

(y+1)(y-3)=y(y+1)-3(y+1)

=y^{2}+ y -3y -3

=y^{2}-2y -3

We can no longer able to simplify further, therefore:

(y+1)(y-3)

=y^{2}-2y -3