Answer:
y=4(1/2)^x
Explanation:
Start with x=0, you know any number to the power of 0 is one. Since y=4, when x=0, you know the coefficient out front must be 4 b/c 4*1=4.
Next, look at x=1, which is equals 2. 1/2^1 = 1/2. Multiply by 4 to get 2. That means that b must equal 1/2. You can check this by looking at x=2. At x=2, y=1. (1/2)^2=1/4. 1/4(4)=1, making 1/2 the b value.