## Wednesday, November 16, 2011

### HP 15C Programming Tutorial - Part 7: Solve and Integration

Solving Equations with the HP 15C

The HP 15C has a powerful solve feature that finds the real roots of the equation f(x)=0 given an interval.

Caution: When using the solve feature on an original HP 15C calculator - you will want to allow additional time since the calculator can be slow in the solve process.

Procedure:
1. Program an equation and label it.
2. In Run mode, enter the lower limit of the interval and press [ENTER].
3. Enter the upper limit of the interval, and press [ f ] [ ÷ ] (SOLVE) Label. Label can be 0-9, .0-.9, or A-E.

We will use two examples to illustrate the power of the SOLVE function.

Example 1

Find the root for the equation f(x) = x ln x - 3. We claim that the root is somewhere in the interval [1, 6].

First enter the equation. For this equation, use Label 0. Assume that x is in the display.

`Key Codes			Key001	42	21	0	LBL 0002			36	ENTER	*  duplicates x003		43	12	LN	*  X: ln(x), Y: x004			20	×	*  x ln (x)005			3	3006			30	-	* x ln (x) - 3007		43	32	RTN`

1. Press [ g ] [R/S] (P/R) to go to Run Mode.
2. Press [ 1 ] [ENTER] [ 6 ] [ f ] [ ÷ ] (SOLVE) [ 0 ].

Result: x ≈ 2.8574.

Example 2

Find the two roots to the equation g(x) = x^2 + 4x - 3. Using Horner's Method, we can rewrite the equation as g(x) = (x + 4)x - 3.

We will use Label 1 for g(x).

`Key Codes			Key001	42	21	1	LBL 1002			36	ENTER	* duplicates x003			4	4004			40	+005			20	× 	* (x + 4)x006			3	3007			30	-	* (x + 4)x - 3008		43	32	RTN`

Let's try to see if we can find a positive root. How about an interval of [0, 3]?

0 [ENTER] 3 [ f ] [ ÷ ] (SOLVE) 1

Result: x ≈ 0.6458.

Are there any roots bigger than 0.6458? Try an interval of [3, 100].

3 [ENTER] 100 [ f ] [ ÷ ] (SOLVE) 1

Result: x ≈ 0.6458 (no different)

How about any roots below 0? Try an interval [-100, 0].

100 [CHS] [ENTER] 0 [ f ] [ ÷ ] (SOLVE) 1

Result: x ≈ -4.6458

So our two roots are x ≈ {-4.6458, 0.6458}.

Integral

The HP 15C also has a built in integral function ( ∫ ). This is useful for finding definite integrals for functions, even when the function is not defined at the end points.

Caution: Just like the Solve function - allow extra time with the Integral function when using the original HP 15C calculators. In addition, using the Integral function requires 23 memory registers to operate. It may be a good idea to clear the program memory prior to entering functions for integration.

Procedure:
1. Enter a function in a program. The program must have a label.
2. Enter the lower limit of integration and press [ENTER].
3. Enter the upper limit of integration and press [ f ] [ × ] ( ∫ ).

We will use two examples to illustrate the Integration feature.

Example 1

Calculate ∫ ( e ^ (-x^2), x, 0, 2). Use Label 2.

`Key Code				Keys001	42	21	2	LBL 2002		43	11	x^2003			16	CHS004			12	e^x	* e^(-x^2)005		43	32	RTN`

Press [ g ] [R/S] (P/R) to switch to Run Mode. Then press [ 0 ] [ENTER] [ 2 ] [ f ] [ × ] ( ∫ ) [ 2 ].

Result: Integral ≈ 0.8821

Example 2

Calculate ∫ ( |sin x|, x, 0, 2π). Use Label 3.

`Key Code				Keys001	42	21	3	LBL 3002		43	8	RAD	* use Radians mode003			23	SIN004		43	16	ABS	* |sin x|005		43	32	RTN`

In Run mode:

0 [ENTER] [ g ] [EEX] ( π ) 2 [ × ] [ f ] [ × ] ( ∫ ) 3

Result: Integral = 4

This concludes Part 7 of the tutorial. In the next part we will use the knowledge of programming functions and equations to calculate derivatives and sums.

This tutorial is property of Edward Shore. © 2011

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