
Kevin B. answered 05/07/19
PhD in Mathematics with 8+ Years of Teaching Experience
Find the exponential function f(x) = abx that passes through (1,12) and (3,48).
To do this, we first plug in the x- and y-values:
12 = ab1 <--> ab = 12
48 = ab3 <--> ab3 = 48
Now, we must proceed to solve for a and b. This requires some brainstorming. Notice that 48 = 12 x 4. So, if we multiply the first equation (ab = 12) by 4, we get the second equation:
4ab = 48
ab3 = 48
So, 4ab = ab3 , and dividing both sides by ab yields 4 = b2. Therefore b = ± 2. Exponential functions must have a positive base. So b = 2. Our function is now
f(x) = a · 2x
Since, ab = 12 and b = 2, we must have a = 6. Therefore, our final answer is
f(x) = 6 · 2x.