Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
A point moves so that the sum of its distances from the lines and is always 8. Find the area enclosed by the locus, and the length of its perimeter. Give the perimeter to 2 decimal places.
Call the moving point , write the rule as an equation, and square to clear any root. gives the perpendicular bisector of : . The distance of from is . If is the midpoint of and , then and . means the slopes multiply to .
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 rule. . With and this is .
Step 2. The shape. In the plane the four cases give the sides of a square with corners and . In the plane the corners are , , and .
Step 3. The area. Both diagonals are 16 long, so the area is .
Step 4. The perimeter. One side joins to , so it is . The perimeter is .
Answer: area , perimeter about .
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