During his math degree, the tutor used a minimal TI scientific. Nowadays, during tutoring, he sees so many calculators with amazing features….

The Casio fx-991ES NATURAL DISPLAY is, in my opinion, comparable to a Sharp WriteView. Their screens are deeper than most scientifics, so that they can display fractions up-and-down. They can also simplify radicals symbolically, like you would by hand: √(40) will display as 2√(10) (in the right mode). Moreover, they can display radian measures symbolically, using pi: sin^(-1)(0.5) will display as π/6 (in rad mode). Sharp summarizes these features as WriteView; Casio describes them as NATURAL DISPLAY.

Those features I will explore in other posts; today I’m showing, with an example, how one might use the equation solver built into the Casio fx-991ES. It’s surprisingly powerful, and surprisingly easy to use:

Example: Solve 11xe^(-0.44x)-1.2sinx + 5 =0

This is likely not an equation most people want to tackle by hand. Here’s how to do it with the Casio fx-991ES:

Step 1: I was in COMP mode to use the solver. That’s MODE 1. Also, I was in rads(Shift Mode 4), which is important: sinx is in the equation.

Step 2: You need to enter the equation as Y=11Xe^-0.44X-1.2sinX+5. Important: to enter the = in the equation, use alpha calc. Use the alpha switch to enter the Y and the X.

Step 3: After you’ve entered the equation, key in shift calc.

Step 4: Y? should now appear. Key in 0, then regular =.

Step 5: Solve for X should now appear. There may already be a number across the bottom; regardless, press regular =.

Step 6: The screen may go blank for a few seconds while the solver works. Soon, though, you’ll be greeted with the solution (if the equation was, indeed, solvable:)). There will be three lines:

1. across the top you’ll see your equation
2. in the middle, you’ll see X=-0.415296339 (for this equation, anyway)
3. across the bottom you’ll see L-R=0 (which, I believe, means “left” minus “right”; it shows how close the solution matches the two sides of the equation).

To double check, I fed the same equation to the solver on my old Sharp EL-520W; it agrees exactly with the Casio’s solution:)

Have fun experimenting!

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.