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Assume f is an exponential function with the two given values. Use the property of exponential functions to calculate values of f(x) for one larger value of x and for one smaller value of x. Then use the calculated and given points to plot the graph.

 

f(5)= 80, f(7)= 64, f(9) = 51.2, f(11) = 40.69

Best Answer 

 #1
avatar+129852 
+5

We have

80 = ab^5  →    a = 80/b^5

And

64 = ab^7  →  a = 64/b^7

Setting  the "a's" equal, we have

80/b^5 = 64/b^7

b^2 = 64/80  = 4/5  = .8

b = √.8 = .894

And solving for "a" we have

80 = a(.894)^5

80 = a(.571)

a = 80/.571 = 140.1

 

So...our function is

f(x) = 140.1 (.894)^x

Here's a graph...https://www.desmos.com/calculator/uvldjauwxm

 

 Mar 4, 2015
 #1
avatar+129852 
+5
Best Answer

We have

80 = ab^5  →    a = 80/b^5

And

64 = ab^7  →  a = 64/b^7

Setting  the "a's" equal, we have

80/b^5 = 64/b^7

b^2 = 64/80  = 4/5  = .8

b = √.8 = .894

And solving for "a" we have

80 = a(.894)^5

80 = a(.571)

a = 80/.571 = 140.1

 

So...our function is

f(x) = 140.1 (.894)^x

Here's a graph...https://www.desmos.com/calculator/uvldjauwxm

 

CPhill Mar 4, 2015

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