Calculating Pi using Series

I am using the formula found here: http://upload.wikimedia.org/math/0/8...67293fb6b0.png

I brake the fractions into 4 parts. A, B, C, D. A is the upper left, B is the upper right, C is the bottom left, and D is the bottom right.

After A, B, and D are calculated by sending a number k=0 through the series (not C, because it is what represents Pi) I proceed to cross multiply to solve for C. I get A*D = B*C

I divide by B, so really, C = AD/B

The output is 3.14159265358973420766845359157829834076… (accurate to 13 digits after the decimal place).

If I go through the series again and repeat the cross multiplication for the next number, k=1, then the output is -167194165969664.18081570948421477548969…

Now, at this point, should I be multiplying my values of C from previous itterations? Or should I be adding them? Or is something wrong with my calculation. Thank you for the advice!