Lol it's quite easy but these questions r annoying me.(adsbygoogle = window.adsbygoogle || []).push({});

The 20th term of an arithmetic series if 131 and sum of the 6th to 10th term inclusive is 235, find sum is the first 20 terms

well

131= a + 19 d 5(2a+ 9d) -3(2a+5d)=235

well i just went on and solve simutalneosly and got the wrong answer for S(20), i don't know how to make it at hte butotm.

2) the sum of 50 terms of an arithmetic is 249 and sum of 49 terms is 233, find 50th term of the series.

249= 50a + 1225d and 233= 49/2 (2a+48d)

and well got the wrong answer aagain.

3) prove [itex]T_n = S_n - S_n_-_1[/itex]

I have no idea how to do that. Thanks

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# Homework Help: Series and Sequence,

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