<p>for sigma notation is there an easier way to figure out the formula instead of guess it ?
1-2+3-4+…</p>
<p>1-2+4-8+…+64</p>
<p>Sure. There are many ways to determine a formula, but it depends on what kind of summation you have. </p>
<p>Give us examples of what type of summation you’re working on.</p>
<p>hi i just edit it can u give me some pointers
i mean if ur way is easier would it help me with all the other problems</p>
<p>Well the last one is a summation of a geometric series with -2 as r.</p>
<p>Use the formula ( 1 - r^n ) / (1 - r). n would be 7.</p>
<p>(1-(-2)^7) / (1-(-2)). You should get 43.</p>
<p>On the TI this can be typed in as:</p>
<p>sigma ((-2)^x, x, 0, 6). Note that we put in n-1 (6) instead of n when we do it with sigma notation.</p>
<p>I believe your first series doesn’t converge and thus there’s no sum for it. It ossillates back and forth between positive and negative. But then again, it’s been quite awhile since I did any kind of series work, so I can’t be exactly sure.</p>