Write the following sum in sigma notation. {{MATH_73}} {{CMD_74}} This one is a little more complicated. We'll worry about the signs later, first we'll deal with the numbers themselves. Do you notice a pattern in the terms? Sure, we get from one term to the next term by dividing by 2. That is: {{ENV_75}} If we call our index variable {{MATH_76}}, then {{MATH_77}} should go from {{MATH_78}} to {{MATH_79}}, and the numbers themselves are just {{MATH_80}}. Now we need to deal with the signs. We say above that {{MATH_81}} will alternate between {{MATH_82}} and {{MATH_83}}. That means, if we multiply the terms we just found by {{MATH_84}}, they will alternate between {{MATH_85}} and {{MATH_86}}. We are starting with {{MATH_87}}, so {{MATH_88}} will give us the alternation starting at the sign we want. {{MATH_89}} {{CMD_90}} {{CMD_91}} Try one on your own. {{CMD_92}} Write the following sum in sigma notation. {{MATH_93}} {{CMD_94}} We write: {{MATH_95}} {{CMD_96}} {{CMD_97}}