inverting data and multiplication

[levelhead]

I have two columns of numerical data, not in any particular order:

A1 B1
A2 B2
A3 B3
... ...

For each row, I need to invert the values in column A and sum the products:

C1 = A1*B1
C2 = (A1*B2)+(A2+B1)
C3 = (A1*B3)+(A2*B2)+(A3*B1)

I can do this by creating a helper column and using INDEX and ROW functions, but I have to modify the function for each row. There are a couple hundred rows of data so that would be very time consuming.

Could someone help me out? Can I do this with just functions or do I need to use visual basic?

thanks