the sum of first 40 terms 1,6,7,13,20.........???????
give slon

• sum for this fibonacci series is S(n)= S(n+2)-S(2)
  so for finding the sum upto 40th term we have to find 42nd term
  f(42)=1095815001 (using C program :p)
  so S(40)= S(42)-S(2)
  S(40)=1095815001-6
  so ans is S(40)= 1095814995
• 11 years agoHelpfull: Yes(5) No(7)
• sry solution is not completed
  
  Sn=n(a1+an)/2
  =40(236)/2
  =40x118
  =4720
  
• 11 years agoHelpfull: Yes(4) No(12)
• sum for this fibonacci series is S(n)= f(n+2)-f(2)(u can check by taking smaller value of n)
  so for finding the sum upto 40th term we have to find 42nd term
  f(42)=1095815001 (using C program :p)
  so S(40)= f(42)-f(2)
  S(40)=1095815001-6
  so ans is S(40)= 1095814995
• 11 years agoHelpfull: Yes(3) No(2)
• as 1+6+7 is sum upto 3rd tem n it is 5th term -6, similarly
  as 1+6+7+13+20+33+53 is sum upto 7th term and is equal to 9th term 139-6=133
  hence sum upto 52nd term is 54th term-6
  using golden ratio we can solve this, bt to be more accurate we calculate a few more terms. 1,6,7,13,20,33,53,86,139,225,364,589,953,1542....
  thus 54th term= 1542*(1.6180339)^40
  hence sum upto 52nd term is 352849113676-6=352849113670
• 11 years agoHelpfull: Yes(3) No(1)
• see,
  1-------sum upto 1st term
  7-------sum upto 2nd term
  14-------sum upto 3rd term
  27-------sum upto 4th term
  47-------sum upto 5th term
  80-------sum upto 6th term
  133-------sum upto 7tht term
  219-------sum upto 8th term
  
  see Sum uptoNth term=(N+2)th term-6 (for this series.)
  
  so sum upto 52th term=54th term-6
  
  1+6+7+13+20+33+53=sum upto 7th term= 9th term-6=139-6
  NOW USING "GOLDEN RATIO" WE CAN FIND THAT
  
  1,6,7,13,...........................,139,225,364,589,953,1542(we have taken here 14TH TERM for accuracy)
  
  so 54th=1542(14th term)*(14th term/13th term)^40
  
  as we considered here 14th terms so the power is (54-14)=40
  so we get,
  1542*(1.6180339)^40=352849113676
  
  so sum upto 52th=54th - 6
  =352849113676 - 6
  =352849113670
• 11 years agoHelpfull: Yes(1) No(0)
• think so the question is mistaken it must be like 1,7,13,20........
  then
  First find the 40th term:
  
  a40 = a1+(n-1)d
  
  given a1=1
  
  d=a2-a1
  
  =7-1
  
  =6
  => a40= 1+39(6)
  = 1+234
  = 235
  Then find the sum:
  
  Sn=(a1+an)/2
  =(1+235)/2
  = 236/2
  = 118
  
• 11 years agoHelpfull: Yes(0) No(28)