A5 inch tall bamboo shoot doubles in height every 3 days. if the equation, y=ab^x where x is the number of doubling periods, represents the height of the bamboo shot, what are the values of a and b?

X-doubling periods
Y-height of bamboo
Y=ab^x

1) make a table of values
X Y
1 5
2 10
3 20

2) write equations and substitute
5=ab^1 —> a=5/b^1 —> a=5/b
10=ab^2

Substitute into second equation

10=(5/b)*b^2
10=5b^2/b
10=5b
b=2

Substitute back in

b=2
10=a*2^2
10=4a
a=5/2

End equation:
Y=5/2*2^x