Question

The number of users on a website has grown exponentially since its launch. After 2 months, there were 90 users. After 4 months, there were 810 users. Find the exponential function that models the number of users x months after the website was launched. Write your answer in the form f(x)=a(b)x.

Answer 1

10(3)^x

Explanation:

The function contains the points (2,90) and (4,810). Use the general form y=abx to write two equations:

90=ab^2 and 810=ab^4

Solve each equation for a:

a=90/b^2 and a=810/b^4

Since a=a, set the other sides of the equations equal and solve for b.

90/b2=810/b4

Cross multiply, then divide and simplify as follows:

90b^4=810b^2

b^4/b^2=810/90

b^2=90

b^3

Now, use the value of b and the point (2,90) to find the value of a.

90=a(3^2)

a=10

So, substitute answers in original equation for a final answer of f(x)=10(3)^x.