Precal Blog

Today in class Mr. B gave us a problem involving exponential functions to work on. This problem stated:

Function f has values f(5)=12 and f(10)=18. Find f(20) and f(x).

First thing we did was create a table. In the X column was 5, 10, and 20. In the f(x) column was 12, 18, and a blank, since we needed to find f(20). Then we used our Add-Multiply method to find b in our a*b^x equation. For this, Mr. B showed us a time saving method we can use for this step. First, we create two equations using the values we know: 12=a*b^5 and 18=a*b^10. Next, we begin substitution to get a=12/b65 and a=18/b^10. Finishing off the substitution method, we are left with one equation: 12/b^5=18/b^10. When we simplify, we get b^5=1.5. Then we find the 5th root of 1.5, and tada! We have our b value for our exponential function equation: 1.08… To find a, we can use the values we already know to set up an equation. This equation is 12=a*1.08…^5. When we solve this out, we find that a=8. Now we have all we need to form our equation. f(x)=8*1.08…^5.

After we finished this, we were given the rest of class to work on claim problems for tomorrow. Mr. B said that he will choose the claim problems from 1-9 in section 2.1 of the packet, so be ready to present tomorrow. The next scribe will be Amie! =D