Given that an is the n-th term of a sequence. If an+1=an+2+2an, a3=−1, and a5=3, then the value of a2 is ...
Explanation
Given the recursive formula for the sequence:
an+1=an+2+2an
We are given a3=−1 and a5=3. We need to find the value of a2.
First, we find the value of a4 by using the recursive formula and substituting n=3 to relate a3, a4, and a5.
a3+1a4=a3+2+2a3=a5+2a3
Substitute the values a5=3 and a3=−1:
a4a4a4=3+2(−1)=3−2=1
Next, we find the value of a2. Since we now have the values of a3 and a4, we can use the recursive formula with n=2 to relate a2, a3, and a4.
a2+1a3=a2+2+2a2=a4+2a2
Substitute the values a3=−1 and a4=1:
−1−1−1−2a2=1+2a2=2a2=2a2=−1
Thus, the value of a2 is −1.