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Thanks, Marco. But, I'm looking for the "Step-by-Step" solution thats is built-in on Wolfram, thats the reason I mentioned it
I don't know if I undestood correctly. How would you calculate this, for example? ![enter image description here][1] [1]: http://community.wolfram.com//c/portal/getImageAttachment?filename=download.png&userId=1300676