Question

Find sum of 12 terms of the series whose nth term is (6n-4):​

Answer 1

Step-by-step explanation:

Refer the attachment for answer

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Answer 2

420 is  sum of 12 terms of the series whose nth term is (6n-4)

Step-by-step explanation:

sum of 12 terms of the series whose nth term is (6n-4)

∑(6n - 4)

= 6 ∑n  - ∑ 4

= 6 (n)(n + 1)/2 -  4n

= 3n(n+1) - 4n

= 3n² + 3n - 4n

= 3n² - n

= n(3n - 1)

n = 12

Sum = 12(3 * 12 - 1)  = 12 * 35  = 420

Another method

1st Term = 6*1 - 4 = 2

2nd term = 6 * 2 - 4 = 8

Last term = 12 th term = 6*12 - 4 = 68

d = common difference = 6

Sum = (n/2)(1st tern + Last term)  = (12/2)(2 + 68)

= 6 * 70

= 420

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