The next task is to make a linear regression

line in order to find the exact

speed at which to throw the balloon. To do this, press

, select the CALC menu, and select item 4: LinReg(ax+b) (Fig. II.1),

Fig. II.1

then press enter twice (Fig. II.2).

Fig. II.2

If your calculator does not display "r" or "r

^{2}," you can press 2nd then 0 to go to the catalog, and select the item "Diagnostic On" and press enter twice. Now repeat the first step.

"r" and "r

^{2}" are used to determine how well the

line fits the data. "r

^{2} " is simply "r" multiplied by itself and is always between 0 and 1. "r" can be any value between -1 and 1. An "r" value of -1 or 1 means you have a perfect fit. As "r" values get closer to 0, the less correlation there is in your data.

Now press

, and clear all the equations. Go to Y

_{1} and press

, select item 5: Statistics... Go to the EQ menu, and select item 1: RegEQ and press enter (Fig. II.3).

Fig. II.3

The

equation should now appear in the Y

_{1} (Fig. II.4).

Fig. II.4

Now, press

, and you should see the regression

line appear over top of the points (Fig. II.5).

Fig. II.5

To find when this

line equals 3, you will have to press

again, and type 3 into the Y

_{2}. Then use the technique learned in "Police and Neon" to find the

intersection of the two lines. The

**x** value of this

intersection is the

speed at which the ball would need to be thrown (Fig. II.6).

Fig. II.6