hp 39g+ (39g & 40g)_mastering the hp 39g+_English_E_F2224-90010

Press and again, choosing Signed

Area… as before. Use the left/right arrow keys

or the key to move the cursor to x = -2.

Press ENTER to accept the starting point.

This time, choose the boundary as F2(X)

instead of the x axis so that we will be finding

the ‘area’ between curves instead of the area

under one. Again, the result will be a signed

area (definite integral) not a true area. See

page 83 for a simple method of finding true

areas.

We now need to choose the end point. This

time do it by tracing with right arrow to move

the cursor. As you do the area will be shaded

by the calculator. The current position is shown

at the bottom of the screen. When you reach

the end point you are looking for, press the

key and the area will be calculated as

before. This is shown right.

To remove the shading, press PLOT again.

Calculator Tip

Note that common sense tells us that the answer is almost

certainly -3.75 rather than -3.75000000002. The small

error is simply due to accumulated rounding error in the

internal methods used by the calculator. For example, an

answer of 0.4999999999 should be read as 0.5. This is

quite common and students should be aware of the need

for common sense interpretation.

Areas between and under curves

If we are wanting to find true areas rather than the ‘signed areas’ given by a

simple definite integral then we must take into account any roots of the

function. This process is shown in detail on page 83, as there are certain

tricks which can be used to make the process far simpler.