MY CART (5)

Use Coupon: CART20 and get 20% off on all online Study Material

ITEM
DETAILS
MRP
DISCOUNT
FINAL PRICE
Total Price: Rs.

There are no items in this cart.
Continue Shopping
Menu
Grade: Select Grade
        
2+7+14+23+.... then find the sum upto 30 terms
5 years ago

Answers : (7)

AUREA
61 Points
							
2, 7, 14, 23, 34 …........ is a series whose common difference is an AP (i.e   5, 7, 9, 11,….).
S= 2 + 7 + 14 + 23 + ……………. An-1 + An
S=       2 +  7  + 14+ 23+………………+An-1  +An
Now, subtracting the equations
0= 2 + { 5 + 7 +9 + 11 +…….+ (n-1)} - An
An= 2+ { (n-1)(5+n-2)}
On simplifying, we get
An = n2+2n-1
Using the summation operator on the series we get
∑An= ∑n+ 2*∑n – ∑1
 where,
∑n2=n(n+1)(2n+1)/6
∑n=n(n+1)/2 and
∑1=n
 
putting n=30 we get the required sum.;)
5 years ago
grenade
2061 Points
							
it is
22-2   +   32-2    +    42-2     till                       312-2
we will get is as 
(∑n2) -1*  – 2(30)                          -1* is taken because n2 starts from 12+22
where
∑n2=n(n+1)(2n+1)/6
 
on substituting the values it will be
 
30*31*61/6   = 9455
so 
9455-1-60
=
9394
approve if useful
5 years ago
grenade
2061 Points
							
i think @ AUREA is it incorrect because 
AUREA forgot  one term in the  APPLIED AGP
pl correct
5 years ago
grenade
2061 Points
							
22-2 = 
2
32-2 =
7
 42-2 
14
52 -2=
23 and so on
 
approve if useful
 
 
 
 
 
5 years ago
AUREA
61 Points
							
 @akshat I think it should be S= ∑{(n+1)2-2}
which simplifies to ∑(n2+2n-1)
5 years ago
AUREA
61 Points
							
putting the value n=30
∑n2=9455
2∑n=930
finally the sum comes to be S=9455+930-30 ,i.e, S=10355
approve if the solution is helpful ; ) 
5 years ago
grenade
2061 Points
							
thanks aurea for correcting me
inspite of n=31 i took it as n=30
the answer would have been 10355 if had placed n=31
sorry
5 years ago
Think You Can Provide A Better Answer ?
Answer & Earn Cool Goodies


Course Features

  • 731 Video Lectures
  • Revision Notes
  • Previous Year Papers
  • Mind Map
  • Study Planner
  • NCERT Solutions
  • Discussion Forum
  • Test paper with Video Solution


Course Features

  • 731 Video Lectures
  • Revision Notes
  • Test paper with Video Solution
  • Mind Map
  • Study Planner
  • NCERT Solutions
  • Discussion Forum
  • Previous Year Exam Questions


Ask Experts

Have any Question? Ask Experts

Post Question

 
 
Answer ‘n’ Earn
Attractive Gift
Vouchers
To Win!!! Click Here for details