Which of these functions represents exponential decay?
f(x)=5(1.2)xf(x) = 5(1.2)^xf(x)=5(1.2)x
f(x)=5(0.8)xf(x) = 5(0.8)^xf(x)=5(0.8)x
f(x)=0.8(5)xf(x) = 0.8(5)^xf(x)=0.8(5)x
f(x)=x5f(x) = x^5f(x)=x5