| Photographers support their cameras on a three-legged structure called a tripod. We ask: why is a support with three legs chosen? Why not two legs? or four? or more? Try to answer these questions before proceeding.
We see that a straight line is determined by ? points. This means that even if our tripod is standing on perfectly flat ground, it will stand steady. However, a quadrapod would most likely wobble, as the plane determined by three of the feet would not necessarily support the fourth. (How many times have you sat on a wobbly chair?) We can also make the above argument algebraically. A straight line in the plane has equation ax + by + c = 0. Although there are 3 coefficients here, only the 2 ratios Similarly, a plane in 3-space has equation |
The tripod
|
 |
