Hello,

Question

I am working on exponential equations of best fit. I have a table numbered from 1-7 with corresponding numbers.
I put that into my calculator and came up with the exponential equation of best fit as y = 8.46(1.42)^x

Now it wants to know how long it will take for 200 items to be sold.

So I know my y is 200 and I set it up as this:

200 = 8.46(1.42)^x

But how do I solve this??
My table only goes up to 7 in my L1 listing, and that is only 96, not 200. So how do I get my L1 to go more than what I have entered?

Thank you.

Answer 1

200/8.46 = 8.46*(1.42)^x/8.46,
23.64 = (1.42)^x,
Log23.64 = x*Log1.42,
X = Log23.64/Log1.42 =

Answer 2

This is in addition to Henry's approach, in case you haven't learned logarithms yet.
I don't know what kind of graphing calculator you are using, but it sounds like you entered the data in the STAT area of your calculator, which is correct for finding the equation.
Now that you have the equation, it should also appear in the "Y=" list, if you saved it there. If you did, you can use the table setup function (TBLSET) and set it to start at any x value, increasing in steps of any value you choose. Then view it (TABLE). That table will display x and y values for your equation and will scroll down to as far as you need.