Graphing and Mathduko

I had planned to post yesterday but we had internet issues both at home and at work.  So I had to wait till this afternoon to do it.
I discovered Mathduko while I was on holidays over Christmas.  It is like suduko but it uses math.  It begins with a 3 by 3 grid and the numbers 1, 2, 3.  It will tell you whether to put a specific number in a square or highlight two to three squares and tell you 6+ which means all three numbers must add up to 6 or 3x which means the two numbers must have a product of 3 or 2 -  meaning when you subtract two numbers, the difference is 2.  From a 3 x 3 grid you move up to a 4 x 4 grid and use the numbers 1 to 4.  I like it in that it is fun and teaches logic. The best thing besides being free is that it works on both iPads and androids.
Today, I was able to incorporate the free graph calc app into two different periods.  We just started graphing quadratics in Algebra II so I had the students graph a quadratic and we took time to go over how to find the x and y intercepts and the vertex using the graph.  I used grapher on my smartboard to show the students how to read their graphs.  Then I had them switch over to the table mode so they could read the numbers to find the vertex and the x and y graphs.  The class went quite fast.
The second class I used it in was College Prep.  I projected some basic exponential functions on the smart board and had the students make observations.  Then I graphed functions such as f(x) = 4^(x+3)  or g(x) = 4^x + 3  or h(x) = -4^x.  The students made observations about each of the graphs and things they had in common.  I had a student ask how I knew it always crossed at (0,1) and I showed them why 4^0 or 7^0 = 1 and why -4^0 is -1.
I gave them 10 problems to work on using the free graph cal and they immediately started doing the problems and seem to truely understand exponential functions.