how many terms of series -1+3+7.... be added to get 95 as sum
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Answered by
6
Hiii friend,
AP = -1,3,7......
Here,
First term (A) = -1
Common difference (D) = 4
Sn = N/2 × [2A +(N-1) × D]
95 = N/2 × [ 2 × -1 + (N-1) × 4]
95 = N/2 × ( -2 + 4N -4)
95 = N/2 × -6+4N
95 = N × -3 + 4N
-3N +4N = 95
N = 95
Hence,
95 term must be taken to get the of 95 as their sum.
HOPE IT WILL HELP YOU...... :-)
AP = -1,3,7......
Here,
First term (A) = -1
Common difference (D) = 4
Sn = N/2 × [2A +(N-1) × D]
95 = N/2 × [ 2 × -1 + (N-1) × 4]
95 = N/2 × ( -2 + 4N -4)
95 = N/2 × -6+4N
95 = N × -3 + 4N
-3N +4N = 95
N = 95
Hence,
95 term must be taken to get the of 95 as their sum.
HOPE IT WILL HELP YOU...... :-)
Anonymous:
It's wrong sister
please check the 3rd last step
please check where is your 2 in 3rd last step...
Answered by
2
Heya!! ✌
➡Here's your answer friend,
Here a(first term) : -1
d(common difference) : 3 - (-1) = 4
Sn = 95
==> Sn = n/2 [2a + (n - 1)d]
==> 95 = n/2 [2 (-1) + (n - 1)4]
==> 95 = n/2 [-2 + 4n -4]
==> 190 = n[ -6 + 4n ]
==> 190 = -6n + 4n²
==> 4n² - 6n = 190
==> 2n² - 3n - 95 = 0
==>by quadratic formula,
==> -b +-√b² - 4ac / 2a
==> -(-3) +- √(-3)² - 4(2)(95) / 2(2)
==> 3 +- √769 / 4
==> x = 3 + 27.73 / 4 or x = 3 - 27.73/4
==> x = 3 + 6.9325 or x = 3 - 6.9325
==> x = 9.9325 approx (9) or x = -3.9325 (neglect)
is the required answer.
Hence, 9th term of A.P. will give sum as 95.
⭐ Hope it helps you : ) ⭐
➡Here's your answer friend,
Here a(first term) : -1
d(common difference) : 3 - (-1) = 4
Sn = 95
==> Sn = n/2 [2a + (n - 1)d]
==> 95 = n/2 [2 (-1) + (n - 1)4]
==> 95 = n/2 [-2 + 4n -4]
==> 190 = n[ -6 + 4n ]
==> 190 = -6n + 4n²
==> 4n² - 6n = 190
==> 2n² - 3n - 95 = 0
==>by quadratic formula,
==> -b +-√b² - 4ac / 2a
==> -(-3) +- √(-3)² - 4(2)(95) / 2(2)
==> 3 +- √769 / 4
==> x = 3 + 27.73 / 4 or x = 3 - 27.73/4
==> x = 3 + 6.9325 or x = 3 - 6.9325
==> x = 9.9325 approx (9) or x = -3.9325 (neglect)
is the required answer.
Hence, 9th term of A.P. will give sum as 95.
⭐ Hope it helps you : ) ⭐
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