SOLUTION: Hi! Find an exponential function passing through (1,3) and (3,4.32) thanks for the study help!

Algebra ->  Functions -> SOLUTION: Hi! Find an exponential function passing through (1,3) and (3,4.32) thanks for the study help!      Log On


   



Question 200454: Hi!
Find an exponential function passing through (1,3) and (3,4.32)
thanks for the study help!

Answer by jsmallt9(3758) About Me  (Show Source):
You can put this solution on YOUR website!
Exponential functions are in the form: y+=+k%2Aa%5Ex where k and a are constants. So our task is to find the values of k and a.

We can do this by using the points we know will fit the equation: (1, 3) and (3, 4.32). Let's start with the first point. Substituting the x and y coordinates from (1, 3) for the x and y in y+=+k%2Aa%5Ex we get:
%283%29+=+k%2Aa%5E%281%29
Simplifying we get:
3+=+k%2Aa
Dividing both sides by a we get:
3%2Fa+=+k

Now let's do it with the second point. We will use the x and y from (3, 4.32) and the "value" we just got for k: 3/a. Substituting these 3 values into y+=+k%2Aa%5Ex we get:
%284.32%29+=+%283%2Fa%29%2Aa%5E3
Simplifying we get:
4.32+=+3a%5E2
Dividing both sides by 3 we get:
1.44+=+a%5E2
Finding the square root of both sides we get:
1.2+=+a or -1.2+=+a
Since we usually want a > 0 then we may reject the a = -1.2.
As a fraction 1.2 is 6/5. If a = 6/5 then k = 3/(6/5) = 5/2. So our exponential equation is:
y+=+%285%2F2%29%286%2F5%29%5Ex or ,as decimals, y+=+2.5%281.2%29%5Ex)