The sum of first n terms of an ap is given by 2 n s = 2n + 3n . find the sixteenth term of the ap and find the ap
Jiyaa1:
hey plz check the ques as it should begin with S 2n and not 2ns
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We have Sn = 2n + 3n
Now replace n by (n-1)
S(n-1) = 2(n-1)² + 3(n-1) = 2n² + 2 - 4n + 3n - 3
= 2n² - n - 1
We know that Sn - S(n-1) = an
therefore 2n + 3n - 2n² + n + 1
an = 6n - 2n² + 1
replace a by 16 we get
a16 = 6 × 16 - 2 × 256 + 1 = - 415...
Now replace n by (n-1)
S(n-1) = 2(n-1)² + 3(n-1) = 2n² + 2 - 4n + 3n - 3
= 2n² - n - 1
We know that Sn - S(n-1) = an
therefore 2n + 3n - 2n² + n + 1
an = 6n - 2n² + 1
replace a by 16 we get
a16 = 6 × 16 - 2 × 256 + 1 = - 415...
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