Question

Find an explicit formula for the following sequence, an which starts with a1=2/3. 2/3,3/4,4/5,5/6,…

Answer 1

Explanation:

a1=2/3

sequence is 2/3,3/4,4/5,...

for numerator a1=2

d=3-2=1

numerator of nth term=a1+(n-1)d=2+(n-1)×1=2+n-1=n+1

denominator = 1 more than numerator=n+1+1=n+2

so an=(n+1)/(n+2)

or for denominator a1=3,d=4-3=1

denominator of nth term=3+(n-1)×1=3+n-1=n+2

an=(n+1)/(n+2)