the algebraic form of the sum of first n terms of an arithmetic sequence is 2n^2+8n.how many consecutive terms of sequence starting form the first are to be added to get 330?
Answers
Answered by
5
Answer:
11
Step-by-step-explanation:
Sum of first n terms is given by 2n² + 8n.
Let 330 be the sum of first k terms.
→ 2k² + 8k = 330
→ 2( k² + 4k ) = 2 x 165
→ k² + 4k = 165
→ k² + 4k - 165 = 0
→ k² + 15k - 11k - 165 = 0
→ k( k + 15 ) - 11( k + 15 ) = 0
→ ( k - 11 )( k + 15 ) = 0
→ k = 11 or - 15
k can't be -ve, so k = 11
Number of terms : 11
Similar questions