**Grade 10: Grain Elevators**

Two tall grain elevators in the distance appear to be the same height though it is known that one (B) is twice the height of the other (A). How can I walk towards them in such a way that they always appear to be the same height.

The students will start by guessing, but what’s really needed is a coordinate system and an equation. We want the locus of a point that is always twice as far from B as from A. It’s a perfect task for grade 10 students who are developing facility with triangle trig and coordinate geometry.

The answer is a circle. Is that a surprise?

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