### Home > CCA > Chapter 7 > Lesson 7.2.1 > Problem7-87

7-87.
1. Find a possible exponential function in y = a · bx form that represents each situation described below. Homework Help ✎

1. Has an initial value of 2 and passes through the point (3, 128).

2. Passes through the points (0, 4) and (2, 1).

Since it has an initial value of 2, the value of a is 2. Substitute this into the general equation y = abx.

Substitute the values 3 for x and 128 for y, then solve for b.

Create two equations substituting the values of the ordered pairs for x and y into the equation y = abx.

Solve the system of equations for a and b.

Be sure you use your results for a and b to write the equation.

$y=4\cdot \left(\frac{1}{2}\right)^x$