Geometric Sequences and Exponential Functions

Key Questions

  • What is the constant ratio "r" mean in a geometric sequence formula?

    It means that the next term can always be obtained by multiplying a current term by #r#.

    #a_1=a#

    by multiplying by #r#,

    #a_2=ar#

    by multiplying by #r#,

    #a_3=ar^2#
    .
    .
    .

    I hope that this was helpful.

    Wataru · 1 · Nov 25 2014
  • How are exponential functions related to geometric sequences?

    Answer:

    Geometric sequences are the discrete version of exponential functions, which are continuous.

    Explanation:

    Geometric sequences are formed by choosing a starting value and generating each subsequent value by multiplying the previous value by some constant called the geometric ratio. If a formula is provided, terms of the sequence are calculated by substituting #n=0,1,2,3,...# into the formula. Note how only whole numbers are used, because it doesn't make sense to have a "one and three-quarterth" term. With an exponential function, the inputs can be any real number from negative infinity to positive infinity.

    Teddy · 1 · Jun 14 2018
  • How do you use the geometric sequence formula to find the nth term?

    A geometric sequence is always of the form
    #t_n=t_"n-1"*r#

    Every next term is #r# times as large as the one before.

    So starting with #t_0# (the "start term") we get:
    #t_1=r*t_0#
    #t_2=r*t_1=r*r*t_0=r^2*t_0#
    ......
    #t_n=r^n*t_0#

    Answer:
    #t_n=r^n*t_0#
    #t_0# being the start term, #r# being the ratio

    Extra:
    If #r>1# then the sequence is said to be increasing
    if #r=1# then all numbers in the sequence are the same
    If #r<1# then the sequence is said to be decreasing ,
    and a total sum may be calculated for an infinite sequence:
    sum #sum=t_0/(1-r)#

    Example :
    The sequence #1,1/2,1/4,1/8...#
    Here the #t_0=1# and the ratio #r=1/2#
    Total sum of this infinite sequence:
    #sum=t_0/(1-r)=1/(1-1/2)=2#

    MeneerNask · 1 · Jan 13 2015
  • What is Geometric Sequences ?

    A geometric sequence is given by a starting number, and a common ratio.

    Each number of the sequence is given by multipling the previous one for the common ratio.

    Let's say that your starting point is #2#, and the common ratio is #3#. This means that the first number of the sequence, #a_0#, is 2. The next one, #a_1#, will be #2 \times 3=6#. In general, we have that #a_n=3a_{n-1}#.

    If the starting point is #a#, and the ratio is #r#, we have that the generic element is given by #a_n=ar^n#. This means that we have several cases:

    1. If #r=1#, the sequence is constantly equal to #a#;
    2. If #r=-1#, the sequence is alternatively equal to #a# and #-a#;
    3. If #r>1#, the sequence grows exponentially to infinity;
    4. If #r<-1#, the sequence grows to infinity, assuming alternatively positive and negative values;
    5. If #-1<r<1#, the sequence exponentially decreases to zero;
    6. If #r=0#, the sequence is constantly zero, from the second term on.
    KillerBunny · 1 · Feb 1 2015

Questions

Exponents and Exponential Functions