Question 883723
First plug in (x,y) = (0,-3)


y = a*b^x
-3 = a*b^0
-3 = a*1
-3 = a
a = -3


Now plug in a = -3, and (x,y) = (4,-48)


y = a*b^x
y = -3*b^x
-48 = -3*b^4
-48/(-3) = b^4
16 = b^4
b^4 = 16
b = 16^(1/4)
b = 2


So a = -3, b = 2 giving us this


y = a*b^x
y = -3*2^x



So the final answer is {{{y = -3(2)^x}}}