Let us analyze the problem step-by-step to understand the relation and find the maximum length of the chain k.
Step 1: Understand the Relation Condition
The relation is given by:
a=2b+1
Every ordered pair (x,y)∈R must satisfy the condition where the first element is 2 times the second element plus 1.
For our given chain of elements:
Notice that as we move down the chain from a1 to ak+1, the values must strictly decrease because each subsequent term is roughly half of the previous term. All elements a1,a2,…,ak+1 must belong to the set A={1,2,3,…,100}.
Step 2: Work Backward from the Smallest Possible Element
To maximize the number of links (k) in our sequence, we should make the final elements as small as possible.
Let the smallest positive integer in the set A be the last element of our sequence, ak+1.
Let us assume the smallest valid positive integer for the final entry is:
ak+1=1
Now, let's build the sequence backward using the relation rule an=2an+1+1:
For the k-th pair (ak,ak+1):
ak=2(1)+1=3
(Pair: (3,1)∈R)
For the previous pair:
ak−1=2(3)+1=7
(Pair: (7,3)∈R)
Moving backward again:
ak−2=2(7)+1=15
(Pair: (15,7)∈R)
Moving backward again:
ak−3=2(15)+1=31
(Pair: (31,15)∈R)
Moving backward again:
ak−4=2(31)+1=63
(Pair: (63,31)∈R)
If we try one more step backward:
ak−5=2(63)+1=127
However, 127∈/A because the set A only contains numbers up to 100. Therefore, 63 must be our starting element (a1).
Step 3: List the Complete Sequence and Count k
Let's align our calculated values with the sequence terms starting from a1=63:
a1=63
a2=31
a3=15
a4=7
a5=3
a6=1
Now, let us write out the resulting ordered pairs in the sequence:
(a1,a2)=(63,31)
(a2,a3)=(31,15)
(a3,a4)=(15,7)
(a4,a5)=(7,3)
(a5,a6)=(3,1)
Counting the total number of ordered pairs in this chain, we get exactly 5 pairs.
Thus, the maximum value of k is 5.
Conclusion
The largest integer k for which such a sequence exists is 5.
Hence, the correct option is (a) 5.