Question

How many terms of the A.P 1,4,7 ----- should be taken so that their sum is 51.​

Answer 1

Answer:

6

Step-by-step explanation:

sum of a.p upto n terms =n/2(2a+(n-1)d)

where a is first term =1

d=common difference =3(in above ques)

51=n/2(2+(n-1)3)gives n= 6

Answer 2

Answer ❤️

A.P. => 1,4,7...

a= 1

d = 4 - 1 = 3

Let the number of terms required to make a sum of 51.

be "n"

so, Sñ = 51

n/2 [2a + (n - 1)d ] = 51

n/2 [ 2 (1) + (n-1) (3) ] = 51

n [2+3n-3] = 51×2

n [3n - 1] = 102

3n² - n - 102 = 0

3n² - 18n + 17 [n - 6] = 0

3n+17 = 0 or n - 6 = 0

n = -17/3 or n = 6

=> Invalid since number of terms can't be negative.

So, n = 6

hence, the number of terms required to make a sum of 51 is 6.

hope help you

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