Mathematics, 01.11.2019 14:31 raekwonpowell10
Find the sum of the first 20 terms of an arithmetic progression of which the third term is 55 and the last term is -98
Answers: 1
![\left[a_{19}+18 d=-98\right]+\left[a_{1}+2 d=55\right]](/tpl/images/0355/7478/306ed.png)
![a_{20}=[1106 / 16]-[2907 / 16]](/tpl/images/0355/7478/d1bb6.png)
![S_{20}=\left[\frac{20\left(\left(\frac{558}{8}\right)+\left(\frac{-1801}{16}\right)\right)}{2}\right]](/tpl/images/0355/7478/61d1b.png)
![S_{20}=\left[\frac{\left.20\left(\frac{1106}{16}\right)+\left(\frac{-1801}{16}\right)\right)}{2}\right]](/tpl/images/0355/7478/41eca.png)
![S_{20}=5\left[\frac{-695}{16}\right]](/tpl/images/0355/7478/8eed1.png)
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Find the sum of the first 20 terms of an arithmetic progression of which the third term is 55 and th...
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