Home
Class 12
MATHS
Sum to n terms the series 4 + 14 + 30 ...

Sum to n terms the series
`4 + 14 + 30 + 52+ 82+ 114+.........`

Text Solution

AI Generated Solution

The correct Answer is:
To find the sum to n terms of the series \(4 + 14 + 30 + 52 + 82 + 114 + \ldots\), we will follow these steps: ### Step 1: Identify the pattern in the series First, we observe the given series: - The first term \(a_1 = 4\) - The second term \(a_2 = 14\) - The third term \(a_3 = 30\) - The fourth term \(a_4 = 52\) - The fifth term \(a_5 = 82\) - The sixth term \(a_6 = 114\) Now, let's find the differences between consecutive terms: - \(a_2 - a_1 = 14 - 4 = 10\) - \(a_3 - a_2 = 30 - 14 = 16\) - \(a_4 - a_3 = 52 - 30 = 22\) - \(a_5 - a_4 = 82 - 52 = 30\) - \(a_6 - a_5 = 114 - 82 = 32\) Next, we find the second differences: - \(16 - 10 = 6\) - \(22 - 16 = 6\) - \(30 - 22 = 8\) - \(32 - 30 = 2\) The second differences are not constant, indicating that the terms are not in a simple arithmetic progression. However, we can see that the first differences are increasing. ### Step 2: Establish a general formula for the nth term We can observe that the nth term appears to be a quadratic function. Let's assume: \[ a_n = An^2 + Bn + C \] We will use the first few terms to set up equations to solve for \(A\), \(B\), and \(C\). Using the first three terms: 1. For \(n=1\): \(A(1^2) + B(1) + C = 4\) → \(A + B + C = 4\) 2. For \(n=2\): \(A(2^2) + B(2) + C = 14\) → \(4A + 2B + C = 14\) 3. For \(n=3\): \(A(3^2) + B(3) + C = 30\) → \(9A + 3B + C = 30\) Now we have the system of equations: 1. \(A + B + C = 4\) (Equation 1) 2. \(4A + 2B + C = 14\) (Equation 2) 3. \(9A + 3B + C = 30\) (Equation 3) ### Step 3: Solve the system of equations Subtract Equation 1 from Equation 2: \[ (4A + 2B + C) - (A + B + C) = 14 - 4 \] This simplifies to: \[ 3A + B = 10 \quad (Equation 4) \] Subtract Equation 2 from Equation 3: \[ (9A + 3B + C) - (4A + 2B + C) = 30 - 14 \] This simplifies to: \[ 5A + B = 16 \quad (Equation 5) \] Now, subtract Equation 4 from Equation 5: \[ (5A + B) - (3A + B) = 16 - 10 \] This simplifies to: \[ 2A = 6 \quad \Rightarrow \quad A = 3 \] Now substitute \(A = 3\) into Equation 4: \[ 3(3) + B = 10 \quad \Rightarrow \quad 9 + B = 10 \quad \Rightarrow \quad B = 1 \] Now substitute \(A = 3\) and \(B = 1\) into Equation 1: \[ 3 + 1 + C = 4 \quad \Rightarrow \quad C = 0 \] Thus, the nth term is: \[ a_n = 3n^2 + n \] ### Step 4: Find the sum to n terms The sum \(S_n\) of the first n terms is given by: \[ S_n = \sum_{i=1}^{n} a_i = \sum_{i=1}^{n} (3i^2 + i) \] This can be separated into two sums: \[ S_n = 3\sum_{i=1}^{n} i^2 + \sum_{i=1}^{n} i \] Using the formulas for the sums: \[ \sum_{i=1}^{n} i^2 = \frac{n(n+1)(2n+1)}{6} \] \[ \sum_{i=1}^{n} i = \frac{n(n+1)}{2} \] Substituting these into the equation for \(S_n\): \[ S_n = 3 \cdot \frac{n(n+1)(2n+1)}{6} + \frac{n(n+1)}{2} \] \[ = \frac{n(n+1)(2n+1)}{2} + \frac{n(n+1)}{2} \] \[ = \frac{n(n+1)(2n+1 + 1)}{2} \] \[ = \frac{n(n+1)(2n+2)}{2} \] \[ = n(n+1)(n+1) \] \[ = n(n+1)^2 \] ### Final Answer Thus, the sum to n terms of the series \(4 + 14 + 30 + 52 + 82 + 114 + \ldots\) is: \[ S_n = n(n+1)^2 \]
Promotional Banner

Topper's Solved these Questions

  • SEQUENCE & SERIES

    RESONANCE ENGLISH|Exercise EXERCISE -1 PART -I RMO|43 Videos
  • SEQUENCE & SERIES

    RESONANCE ENGLISH|Exercise EXERCISE -1 PART -II RMO|1 Videos
  • SEQUENCE & SERIES

    RESONANCE ENGLISH|Exercise EXERCISE -2 (PART-II : PREVIOUSLY ASKED QUESTION OF RMO)|3 Videos
  • RELATION, FUNCTION & ITF

    RESONANCE ENGLISH|Exercise SSP|55 Videos
  • TEST PAPER

    RESONANCE ENGLISH|Exercise MATHEMATICS|48 Videos

Similar Questions

Explore conceptually related problems

Sum up to n terms the series

Find the sum of n terms of the series 1^2 + 4^2+ 7^2 + .........

Sum to n terms the series : 7+77+777+...

Sum to n terms the series 1+3+7+15+31+...

Sum to n terms the series 7+77+777+....

Sum to n terms the series 1 + (1+ 2) + (1 + 2 + 3) + (1 + 2 + 3 + 4).......

Find the sum of n terms of the series 1 + 9 +24 + 46 + 75.........................

Find the n^(th) term and sum to n terms of the series 8, 14, 22, 32, 44,.....

Sum to n terms the series : 0.7+0.77 + 0.777+ ....

Find the sum of n terms of the series 1*2*3+2*3*4+3*4*5...........

RESONANCE ENGLISH-SEQUENCE & SERIES -SELF PRACTICE PROBLEMS
  1. Find the sum of first 16 terms of an A.P. a (1), a (2), a(3)……….. If...

    Text Solution

    |

  2. There are n A.M. s between 3 and 29 such that 6th mean : (n - 1) th me...

    Text Solution

    |

  3. For what value of n , (a ^(n +3) + b ^(n +3))/(a ^(n +2) + b ^(n +2)),...

    Text Solution

    |

  4. about to only mathematics

    Text Solution

    |

  5. If x ,2y ,3z are in A.P., where the distinct numbers x ,y ,z are in G....

    Text Solution

    |

  6. A G.P. consist of 2n terms. If the sum of the terms occupying the odd ...

    Text Solution

    |

  7. If the continued product of three numbers in G.P. is 216 and the sum o...

    Text Solution

    |

  8. Find the value of n so that (a^(n+1)+b^(n+1))/(a^n+b^n) may be the geo...

    Text Solution

    |

  9. If a = underset(55 "times")underbrace(111.....1), b= 1+10+10^(2)+10^(3...

    Text Solution

    |

  10. If a,b,c,d,e are five numbers such that a,b,c are in A.P., b,c,d are i...

    Text Solution

    |

  11. If the ratio of H.M. between two positive numbers 'a' and 'b' (a gt b)...

    Text Solution

    |

  12. (i) a , b, c are in H.P. , show that (b + a)/(b -a) + (b + c)/(b - c)...

    Text Solution

    |

  13. If a,b,c ,d are in H.P., then show that ab + bc + cd =3ad

    Text Solution

    |

  14. If 4 + (4 +d)/( 5) + (4 + 2d)/(5 ^(2)) ……….=1, then find d.

    Text Solution

    |

  15. Evaluate :1 + 3x + 6x ^(2) + 10 x ^(3)+……. upto infinite term, whre |x...

    Text Solution

    |

  16. Sum to n terms of the series :1 + 2 (1 + (1)/(n)) + 3 (1 + (1)/(n )) ^...

    Text Solution

    |

  17. Sum to n terms the series (3)/(1 ^(2) . 2 ^(2)) + (5)/( 2 ^(2) . 3 ^...

    Text Solution

    |

  18. Sum to n terms the series 1 + (1+ 2) + (1 + 2 + 3) + (1 + 2 + 3 + 4)...

    Text Solution

    |

  19. Sum to n terms the series 4 + 14 + 30 + 52+ 82+ 114+.........

    Text Solution

    |

  20. If sum (r =1) ^(n ) T (r) = (n +1) ( n +2) ( n +3) then find sum ( r ...

    Text Solution

    |