Deriviation of equation 3

So this blog is about how to derive equation 3 from the two parent equations we already have.
So from a(delta)t= V2-V1 we isolate V2 to get V2=a(delta)t+V1---> we will call this :)
Now we substitute :) into another equation we already know from the graph which goes like
d=1/2(V1+V2)*(delta)t
then we get somthing like this and simplify it
d=1/2(V1+a(delta)t+V1)*(delta)t
d=1/2(2V1+a(delta)t)*(delta)t
d=V1(delta)t+1/2a(delta)t^2


So that was it.
pretty easy huh.
I know