411 REFERENCE · Wikibooks
Puzzles/Geometric Puzzles/Rectangle and Circle/Solution
Reference material by Wikibooks contributors. This retains its source identity and is not 411 news reporting.
Answer
30 inches
Tools Used to Solve
Pythagorean Theorem
Quadratic Formula
Solution
center
Given:
Find:
We realize that every point on a circle is equidistant from the origin. This implies
that the rectangle's corner touching the circle must be r inches away from the origin, where r is the radius. We can then draw a right triangle with sides and Now apply the Pythagorean Theorem to this triangle and solve for r.
The above equation is quadratic and can be solved by applying the
Quadratic Formula.
Which simplifies to,
Now we can plug in our numbers and solve,
or
Thus the radius of our circle is 30 inches. Notice that 6 inches is not a valid answer. Why?
Comment: Simply making a statement that "we can then draw..." is confusing. Need more explanation on why r-x and r-y are valid descriptors for the triangle sides. This is easier to see with the r-x side than with the r-y.