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Find 26th term from last of an AP 7, 15, 23……., 767 consits 96 terms - Mathematics

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Sum

Find 26th term from last of an AP 7, 15, 23……., 767 consits 96 terms

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Solution

Method: I

rth term from end is given by

= Tn – (r – 1) d or

= (n – r + 1)th term from beginning where n is total no. of terms.

m = 96, n = 26

∴ T26 from last = T(96-26+1) from beginning

= T_71 from beginning

= a + 70d

= 7 + 70 (8) = 7 + 560 = 567

Method: II

d = 15 – 7 = 8

∴ from last, a = 767 and d = –8

`∴ T_26 = a + 25d = 767 + 25 (–8)`

= 767 – 200

= 567.

Concept: Arithmetic Progression
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