A plane is divided into 79 regions by several number of straight lines. How many number of lines is required atleast for this division?

• Ans. 12
  explanation :
  2 lines divide a plane in 4 region
  3 lines divide a plane maximum of 7
  4 lines divide in maximum of 11
  similarly 5 lines 16
  6 lines 22
  ...
  difference b/w 3 lines and 2 lines =3
  diffenece b/w 4 lines and 3 lines = 4
  diference b/w 5 lines and 4 lines = 5
  ....
  after analyse
  ....
  for 2 lines=4 division
  for 3 lines = 7 =4+3
  for 4 lines = 11 =7+4
  for 5 lines = 16=11+5
  for 6 lines = 22=16+6
  for 7 lines = 29=22+7
  for 8 lines = 37=29+8
  for 9 lines = 46=37+9
  for 10 lines = 56=46+10
  for 11 lines = 67=56+11
  for 12 lines= 79=67+12
• 11 years agoHelpfull: Yes(3) No(0)
• @Divya g
  12 is minimum no. of lines if there is no such option than answer will be the next no. after 12 i.e. according to your option answer will be 13.
• 11 years agoHelpfull: Yes(2) No(0)
• 9*9=81 the least perfect square greater than 79
  9+9=18 lines
• 11 years agoHelpfull: Yes(0) No(0)
• the options for this question are:
  a)10
  b)9
  c)13
  d)15
  
  @BHOLANATH : ur explanation is ryt but there is no such option.
• 11 years agoHelpfull: Yes(0) No(0)
• n(n+1)/2 +n -(n-1) =79
  n=12.
  1 line divide = 2 regions
  2 line divide = 4 regions
  3 line divide = 7 regions (max)
  4 line divide = 11 regions(max)
  .
  .
  12 line divide =79 regions(max) :)
  
  
• 11 years agoHelpfull: Yes(0) No(0)
• it is 78 lines because if i make 78 lines then 79 regions are possesed
• 11 years agoHelpfull: Yes(0) No(2)