Answer:
he arithmetic sequence ai is defined by the formula: a1= 2 ai= ai - 1 -3 find the sum of the first 335 terms in the sequence
Step-by-step explanation:
In an arithmetic sequence,
a_1=2a
1
=2
a_i=a_{i-1}-3a
i
=a
i−1
−3
To find:
The sum of the first 335 terms in the given sequence.
Solution:
The recursive formula of an arithmetic sequence is:
a_i=a_{i-1}+da
i
=a
i−1
+d ...(i)
Where, d is the common difference.
We have,
a_i=a_{i-1}-3a
i
=a
i−1
−3 ...(ii)
On comparing (i) and (ii), we get
d=-3d=−3
The sum of first i terms of an arithmetic sequence is:
S_i=\dfrac{i}{2}[2a+(i-1)d]S
i
=
2
i
[2a+(i−1)d]
Putting i=335,a=2,d=-3i=335,a=2,d=−3 , we get
S_{335}=\dfrac{335}{2}[2(2)+(335-1)(-3)]S
335
=
2
335
[2(2)+(335−1)(−3)]
S_{335}=\dfrac{335}{2}[4+(334)(-3)]S
335
=
2
335
[4+(334)(−3)]
S_{335}=\dfrac{335}{2}[4-1002]S
335
=
2
335
[4−1002]
S_{335}=\dfrac{335}{2}(-998)S
335
=
2
335
(−998)
On further simplification, we get
S_{335}=335\times (-499)S
335
=335×(−499)
S_{335}=-167165S
335
=−167165
Therefore, the sum of the first 335 terms in the given sequence is -167165.
