Originally Posted by

**tokio** $\displaystyle

\sum _{k=7}^{77} = \frac{(k)sin(\pi)}{2} + \frac{cos(\pi)}{2}

$

Here is my logic, not sure if its 100% concrete. Let z = $\displaystyle \frac{(k)sin(\pi)}{2} + \frac{cos(\pi)}{2} $

then the first term of k will be 7.. 8 ... 9 .... 77. Obviously summing this up one at a time would be a daunting calculating task which is prone to error. So, im looking for a quicker way to do it. Since we can assume that i is incrementing by one each time and i use the formula n(n+1)/2 and then multiply it by the equation given? If thats the case, i got 3003 when i did that, but this seems like too large of a number to multiply this fraction by. Any suggestions?