# Formula for this summation expression

#### hoopeht

##### New Member
Trying to calculate this in vba: a(), b(), and c() are all arrays whose indexes go from 1 to 10. I know the values of array a and b. I need to calculate values of array c. The values are calculated as following:

c(1) = a(1) * b(1)
c(2) = a(1) * b(2) + a(2) * b(1)
c(3) = a(1) * b(3) + a(2) * b(2) + a(3) * b(1)
...
c(10) = a(1) * b(10) + a(2) * b(9) +...+ a(9) * b(2) + a(10) * b(1)

Instead of writing out the ten equations one by one, is there an easier way to do this?

### Excel Facts

How to change case of text in Excel?
Use =UPPER() for upper case, =LOWER() for lower case, and =PROPER() for proper case. PROPER won't capitalize second c in Mccartney
You'd probably want to do it the way you are doing it.

From a maintenance standpoint, it's easier. "Simplifying" it would probably involve the evaluate function and a formula that would be complex enough to require more comments reminding yourself what you did than would be worth it.

I'm a big fan of explicit coding though.

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