Computing common logarithms on the basis of a few successive square roots of 10 reinforces rules of logarithms and powers for secondary school students.

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### Rose Sinicrope and Daniel V. Bellittiere

The orbits of planets about the sun and satellites about the earth are elliptical. The shape of the orbit can be described by its eccentricity and can be modeled algebraically and graphically. The exploration of orbits enriches our understanding of the mathematical representations, definitions, and connections for ellipses.

### Bryan C. Dorner

Students who have grown up with computers and calculators may take these tools' capabilities for granted, but I find something magical about entering arbitrary values and computing transcendental functions such as the sine and cosine with the press of a button. Although the calculator operates mysteriously, students generally trust technology implicitly. However, beginning trigonometry students can compute the sine and cosine of any angle to any desired degree of precision using only simple geometry and a calculator with a square root key.

### Douglas Wilcock

Can you imagine riding a tricycle with square wheels? Can you imagine that this tricycle would give you as smooth a ride as a traditional tricycle? A *New York Times* article (Chang 2011) described a tricycle that had square wheels but that could be ridden “smoothly around a circular path ridged like a flower's petals.” It then explained that the ridged surface on which the tricycle rode undulated such that “the tricycle's axles—and the rider—remain in the same height as they move.”

### Mara G. Landers

A measurement-based activity can help students struggling to understand trigonometric functions.

### Sheldon P. Gordon

In the climactic scene in The Wizard of Oz, Toto draws back the curtain to expose the Wizard of Oz, and Frank Morgan admits, “I am really a very good man but just a poor wizard.” This statement is reminiscent of Arthur C. Clarke's famous third law: “Any sufficiently advanced technology is indistinguishable from magic” (Clarke 1962, p. 36). For almost all students, what happens when they push buttons on their calculators is essentially magic, and the techniques used are seemingly pure wizardry.

### Sheldon P. Gordon

We tell students that mathematical errors should be avoided, but understanding errors is an important tool in developing numerical methods.

### Alan Sultan

Robots are used in all kinds of industrial settings. They are used to rivet bolts to cars, to move items from one conveyor belt to another, to gather information from other planets, and even to perform some very delicate types of surgery. Anyone who has watched a robot perform its tasks cannot help but be impressed by how it works. Here we offer some insight into the mathematics that goes into designing such a robot.

### Maureen MacInnis

When each student has become part of an ordered pair, we go outside to the school parking lot, where I chalk the outline of a Cartesian plane.

### Nicholas H. Wasserman

The practice of problem posing is as important to develop as problem solving. The resulting explorations can be mathematically rich.