Question

the sum of n terms of an AP is 7n²-5, find the 20th term​

Answer 1

Answer:

363

Step-by-step explanation:

given, sum of n terms of AP = 7n²-5

To find 1st terms (a) of AP, simply put n=1 in above expression

a = 7*1² - 5 = 2

Sum of 2 terms of AP is = 7*2² - 5 = 23

so, 2nd terms of AP = Sum of 2 terms - first term

= 23 - 2 = 21

So, common difference (d) = 2nd term - 1st term

d = 21 - 2 = 19

using formula of nth term of AP T(n) = a + ( n - 1)d

therefore, T(20) = 2 + ( 20 - 1 )19

= 363 Ans

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