One of the important question from the book -ML aggarwal( avichal publication)class 10th , chapter9, arithmetic progression ……..
This type of question has been asked in paper. so please solve it in detail.
Find the A.P. whose nth term is 7-3n.Also find the 20th term
Rajan@2021Guru
Find the A.P. whose nth term is 7-3n.Also find the 20th term
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Let first term of AP be, a
Common difference be d
According to question,
nth term is => 7−3n=a+(n−1)d
=> a+nd−d=7−3n
By comparing coefficents, we get
a=4 & d=−3
So, sum first 25 terms,
2n[2a+(n−1)d]
=> 225[2×4+(25−1)(−3)]
=> 225[8−72]
=> −400