11. Rewrite given summations to the suggested form (finish the dots). Do not evaluate the summations. a) \( \sum_{k=10}^{50} k=\sum_{\dddot{k}=1} \ldots \) b) \( \sum_{k=15}^{77} 7^{k}=\sum_{\dddot{k}=0} \cdots \) c) \( \sum_{k=-10}^{10} k^{2}=\sum_{\dddot{k}=1} \cdots \) d) \( \sum_{k=-10}^{25} j=\sum_{\dddot{k}=1} \ldots \)