1+9+24+46+...

• S = 1+9+24+46+...
  S = 1+ 9+24+46+...
  --------------------------------------------------
  S – S = 1 + 8 + 15 + 22 + ... n terms - Tn
  => Tn = n/2[2 + (n-1)7] = (7n^2 – 5n)/2
  => S = ∑Tn = [7*∑n^2 - 5*∑n]/2
  = 7n(n+1)(2n+1)/12 – 5n(n+1)/4
  = n(n+1)/4 *(14n + 7 – 15)/3
  => S = n(n+1)(7n-4)/6
• 10 years agoHelpfull: Yes(3) No(0)
• 9-1=8
  24-9=15 //8+7=15
  46-24=22 //15+7=22
  NEXT NO.=22+7+46=75
• 10 years agoHelpfull: Yes(1) No(0)
• 75...
  because
  9-1=8
  24-9=15
  46-24=22
  so now,
  8-15=7
  15-22=7
  there is common difference that is 7
  22+7=29
  after that add this 29 with 46
  29+46=75
• 10 years agoHelpfull: Yes(1) No(0)
• 75
  
  9-1=8
  24-9=15
  46-24=22
  and
  15-8=7
  22-15=7
  
  therefore 22+7=29 and 29+46=75
• 10 years agoHelpfull: Yes(0) No(1)
• Tn = n/2[2* + (n-1)7] = (7n^2 – 5n)/2
  Rakesh how come there 2*??? can u explain....
• 10 years agoHelpfull: Yes(0) No(0)
• 1^2=1
  3^2-0=9
  5^2-1=24
  7^2-3=46
  9^2-5=76
• 10 years agoHelpfull: Yes(0) No(0)