Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
A small buoy is tied to a rope and moves in a lake, with all distances in metres. A coordinate system has its origin at the anchor. The buoy is at the point when a control knob is set to the number . The operator wants the buoy to be exactly from the anchor. This happens for two values of . Write the square of the distance from the origin as a quadratic expression in and set it equal to . Solve for . Give the positive value of and the negative value of . Then say in which octant the buoy sits for the negative value, as a number from 1 to 8.
The distance from the -axis is , and the other axes follow the same pattern. The distance from the plane is .
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The equation. . Setting it equal to gives , so .
Step 2. Solve. , so or .
Step 3. The positions. For the buoy is at . For it is at .
Step 4. The octant. The signs give octant VII, which is octant number .
Check. For the distance is . For it is .
Answer: or , and for the buoy is in octant VII.
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