Question

Explain the

The fifth term of a non-linear sequence is 324. The term-to-term rule is ‘multiply by 3?
Work out the second term of the sequence.
Explain the method you used to solve this problem.

Answer 1

a2=12 (the second term of the sequence is 12)

Explanation:

a5=324

If the term to term rule is multiply by any number, we deal with geometrical sequence

The formula you should use is an= a1*r^(n-1) where n is the number of the term which we know. In our case we know

a5, so use 5 instead of n

Then you have a5=a1*r^4 where r is the number 3 (because each next term is greater than previous in 3 times)

a5=324

324= a1*3^4

324=a1*81

a1=4 (We find the first term of sequence, because having it you can easily search for every term )

Return to the formula an= a1*r^n-1

Now search for the second term using 2 instead of n in the formula

a2= a1*r^1

a2=a1*r, a1=4, r=3

a2=4*3=12