Posted by Jake on Sunday, February 19, 2012 at 5:55pm.
if f is an exponential function, and f(5)=20 and f(9) = 14, use the addmultiply property to calculate f(13),f(17), and f(21). Show your method

Math  bobpursley, Sunday, February 19, 2012 at 6:08pm
there is a difference of x=+4 between 5, 9
There is a multiply difference of 14/20=.7 between the two.
f(13)=14*.7
f(17)=14*.7*.7
f(21)=14(.7*.7*.7)

Math  Reiny, Sunday, February 19, 2012 at 6:09pm
let f(x) = a(b^x) or
y = a(b^x)
given: when x=5, y=20
20 = a b^5
given: when x=9, y=14
14 = a b^9
divide the 2nd by the first:
b^4 = 14/20 = 0.7
b = (0.7)^.25 = appr .91469
sub into 20 = a b^5
20 = a(.91469)^5
a = 31.236
f(x) = 31.236 (.91469)^x
f(13) = 31.236(.91469)^13 = 9.8
you do the buttonpushing for the rest
Note, I used the memory locations of my calculator to store all the supplied decimal values for both a and b
Answer This Question
Related Questions
 math5  Which choice is the answer? Show me please. Tara spent 3 hours doing ...
 Distributive property  How would I multiply these expression? 6(h4) 3(x+8) ...
 Math question? :c  Use the Distributive Property to multiply. Show all steps. 7...
 algebra 2  It says to: Use the Distributive Property to show that the following...
 Math  Let f(t) be an exponential function with f(0) = 11 and f(4) = 59. Use the...
 Calculus  Given y=log(x), what is dy/dx? If you have to derive this from first ...
 math5  Tara spent 3 hours doing homework. She spent 1/3 of her time on math, ...
 5th Grade math  What is a partialproducts algorithm. For example 87*65=? How ...
 Math. idk?  6. Name the like terms in the following expression. 5m + 4 + 3m + ...
 math  1.Transform the graph of f(x) = 3^x to sketch g(x) = 3^(x+1) 2. Show ...
More Related Questions