Question 468011
  <pre><font face = "Tohoma" size = 4 color = "indigo"><b> 
Hi,
find the cardinal number for the set
B={1,3,5,...,21}  |arithmetic sequence where d = 2
{{{a[n]=a[1]+(n-1)*d}}}
{{{21= 1+(n-1)*2}}}
   21 = 2n- 1
   22 = 2n
   11 = n, 21 is the 11th term, that is, this set has 11 terms 
  cardinal number for this set is 11