Hello again. More homework you say! Yes I'm afraid so. Thanks very much for people's feedback from the first lesson.

When it comes to teaching maths, my class always seems to get me involved, so this second instalment of TiGM homework is going to be very humbling for me. So let's get it over and done with. Grab your coffee, make yourself comfortable and let's get started.

Lesson 2
So you think to yourself, it is time to lose some weight. You go and get some professional advice and the first thing they do is find your Body Mass Index (BMI) - a very simple method to approximate your size (underweight, average, overweight, obese). The formula they use is:

The values fall into the following categories for adults (1 dec. pl).

Once again, have a look at the important buttons we will be using this lesson (right).

Part 1 - Entering an equation
Grab your calculator and turn it on. Enter EQUA mode by using the arrows on your keypad and press the blue EXE button (figure 1). We are going to use Solver mode (F3) (figure 2).

Let's enter the equation 'B equals M divided by H squared' (figure 3). The letters are those red letters you can see above the buttons on your keypad. You can enter the letters by pressing the red ALPHA button before pressing each letter. The 'squared' button is in the second row and the 'equals sign' is above the decimal point. Notice it is in yellow so you have to use SHIFT button instead of ALPHA. The end result should look like figure 3. Notice after you pressed EXE, all the variables were listed below the equation, ready for you to enter values. You will most likely have different values to mine though.

Part 2 - Entering values for the variables
Now the bold, horizontal cursor should be on the letter B (figure 4). You can move this cursor by pressing the up and down arrow on your keypad. Try this now. Okay, let's enter the values for each variable. I'll be the guinea pig for this example. Let us find out my BMI.

Now the first variable is B. Since this is the variable we are looking for, set it to 0 by pressing 0 then EXE. (it could be any value, but 0 seems the neatest. Beware that is is sometimes not a good value, but I'll explain why later). Next is M (in kg), which is 110 ... And lastly is H (in m) which is 1.93 (figure 4). Move the cursor back up to B, since this is the variable we want to solve for (figure 4). Now press SOLV (F6) and the answer is ... 29.5! ... (figure 5) I actually went and found another calculator to make sure it was right! It is at this point I feebly remind myself that muscle weighs more than fat. I think this means I need to grow some more!

Part 3 - Solve different for variable
Alright, so I have some work to do. What weight should I be then? Well realistically, I could try to get myself into the upper ranks of normal. So let's say my BMI is 25.0. If you haven't already, press EXIT (below the grey MENU key) to return to our equation. We are going to set B to 25, change M to 0 and leave H as 1.93 (figure 6). Move your cursor to M and press SOLV (F6). My 'ideal' weight is 93kg (figure 7).

I'll keep you posted.

Here are some links for reading about BMI and charts for kids.

• Health Insite

You will most likely enjoy putting in your own values. Of course please feel free to email me if you are unsure of any parts.

Part 4 - How does the calculator solve equations?
Above I mentioned that we set the variable we wish to find to 0. Now to solve these equations, the calculator uses Newton's method with the initial value being whatever number we put in. Because of this, there are limitations and sometimes errors when using SOLVER. According to the manual (p. 108), '[d]ue to certain characteristics of Newton's method, solutions for the following types of functions tend to be difficult to calculate.

• Periodic functions (eg. y = sinx),
• Functions whose graph produces sharp slopes (eg. y=1/x),
• Inverse proportion expressions and other discontinuous functions.'

If an error does occur, you might like to try another value.

Well done.

Marty Schmude