Expert: Sherman D. - 8/21/2009

Question
hello,

i've been busting my brain trying to find out the equation rule to these to functions.

1)
x(weeks) - y(infected)
1 - 3
2 - 15
3 - 75
4 - 375

2)

x(years) - y(ships)

1990 - 100
1991 - 145
1992 - 190
1993 - 235

i was thinking that for the 2nd problem that to just look at the last didgit( 0,1,2,3) and i think the eqation would be x times 45 plus 100  is that correct?

thank you for helping :D  

Answer
if you are saying you have the values

1,3
2,15
3,75
4,375

then

its like saying 3,15,75,375 of a sequence in this case

a(n) = 3 * r^(2 - 1)
15 = 3r
r = 5

a(n) = 3 * 5^(n - 1)

to put it another way

y = 3 * 5^(x - 1)

Thats a geometric sequence

-----------------------------------------------

1990, 100
1991, 145
1992, 190
1993, 235

again, but think of this was the years from 1990 on as

0, 100
1, 145
2, 190
3, 235

as you can tell, the problem would be

a(n) = 45n + 100

or in your case y = 45x + 100