Average in a summation

Say I have an Excel File with X and Y columns.

How can I compile a program to do the (average between 2, X terms) times (the difference between the 2, Y terms) for n number of terms in consecutive order.

I tried Sum([X(1:end-1) + X(2:end)]/2.* (y(2:end)-Y(1:end))) for some reason the actual value was half the amount from what I got so I'm not sure if I made and error in my coding.

Answer 1

[Azzi Abdelmalek]

You did 2 errors

X=rand(10,1);
Y=rand(10,1);
sum((X(1:end-1)+X(2:end))/2.*(Y(2:end)-Y(1:end-1)))

sum instead of Sum

Y(2:end)-Y(1:end) is not correct (different sizes)