Question

Find the exponential function that passes through the points (1, 3) and (2, 9). A) y = 12x B) y = 9x C) y = 6x D) y = 3x

Answer 1

y = 3x

Substitute the two points into the equation y = abx, giving 3 = ab1 and 9 = ab2.

Since a = a, then

3

b1

=

9

b2

, rearranged yields 3b2 = 9b1 → 3b2 − 9b = 0 → b(3b − 9) = 0

Thus, b = 0 or b = 3.

A curve of exponential function never drop below the x-axis, ignore any values of b that are less than or equal to zero.

Therefore, insert b = 3 into

3

b1

= a and

9

b2

= a → a = 1 for both equations.

y = abx

y = (1)(3x)

y = 3x

Answer 2

D

Explanation:

An exponential function which crosses through (1,3) and (2,9) will have a base of 3 since the y values are multiples of 3.

3^1 = 3

3^2 = 9

This means that the function is y = 3^x.