CBSE Class 10 Answered
Q no 7 and 8 solve both![](https://images.topperlearning.com/topper/tinymce/imagemanager/files/8c58afcda608a00693a93130603039245a1a4533cffd34.5805876720171113072509.jpg)
![](https://images.topperlearning.com/topper/tinymce/imagemanager/files/8c58afcda608a00693a93130603039245a1a4533cffd34.5805876720171113072509.jpg)
Asked by sucharitasahoo1 | 26 Nov, 2017, 10:09: AM
![begin mathsize 16px style straight S subscript straight n equals end subscript straight n over 2 left parenthesis 2 straight a plus left parenthesis straight n minus 1 right parenthesis straight d right parenthesis
straight n over 2 left parenthesis 2 straight a plus left parenthesis straight n minus 1 right parenthesis straight d right parenthesis equals 1 half left parenthesis 5 straight n squared plus 3 straight n right parenthesis
2 straight a plus left parenthesis straight n minus 1 right parenthesis straight d equals left parenthesis 5 straight n plus 3 right parenthesis
2 straight a minus straight d plus nd equals 5 straight n plus 3
comparing
straight d equals 5
2 straight a minus straight d equals 3...... straight a equals 4
sub
straight t subscript 40 equals straight a plus 39 straight d end style](https://images.topperlearning.com/topper/tinymce/cache/b5bcb153ef3f1c1a633a6761cc49b536.png)
Answered by Arun | 26 Nov, 2017, 17:12: PM
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