# Find the sum: 4-1n+4-2n+4-3n+... upto n terms - Mathematics

Sum

Find the sum: 4 - 1/n + 4 - 2/n + 4 - 3/n + ... upto n terms

#### Solution

Here, first term, a = 4 - 1/n

Common difference,

d = (4 - 2/n) - (4 - 1/n)

= (-2)/n + 1/n

= (-1)/n

∵ Sum of n terms of an AP,

S_n = n/2[2a + (n - 1)d]

⇒ S_n = n/2[2(4 - 1/n) + (n - 1)((-1)/n)]

= n/2 {8 - 2/n - 1 + 1/n}

= n/2(7 - 1/n)

= n/2 xx ((7n - 1)/n)

= (7n - 1)/2

Concept: Sum of First n Terms of an A.P.
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#### APPEARS IN

NCERT Mathematics Exemplar Class 10
Chapter 5 Arithematic Progressions
Exercise 5.3 | Q 21.(ii) | Page 53
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