Question

- The
Sum
first in n terms of an Ap
is 2n2 +n find the nth term and common
difference of the A-p
​

Answer 1

Answer:

Sum of first n terms of AP, Sn = 2n2 + 5n Now choose n =1 ... second term = 18-7 = 11 So common difference becomes, ...

Missing: +n

Answer 2

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Answer:

Sum of first n terms of AP, Sn = 2n2 + 5n Now choose n =1 and put in the above formula,First term = 2+5 = 7 Now put n=2 to get the sum of first two terms = 2x4 + 5x 2= 8 + 10 = 18 This means  first term + second term = 18 but first term =7 as calculated above so, second term = 18-7 = 11 So common difference becomes, 11-7 = 4 So the AP becomes, 7, 11, 15, ....nth term = a + (n - 1)d = 7 + (n-1)4 = 7 + 4n - 4 = 3 + 4n