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Wednesday, April 23, 2014

Circle - Rectangle Problems

Category: Plane Geometry

"Published in Newark, California, USA"

The quarter mile race track shown in the figure has parallel sides AB and CD, each 315 ft. long. If the ends are semicircles, find the area bounded by the track. If a race is run from S to D by way of C, find the length of the race in yards, given that arc SC = 44/67 x arc AC. (1 mile = 5280 ft.)

Photo by Math Principles in Everyday Life

Solution:

The quarter mile race track consists of  two semicircles and a rectangle. Let's divide the given figure as follows


Photo by Math Principles in Everyday Life

Let T = be the total distance of a race which is equal to 0.25 miles
      d = be the diameter of the semicircles
      C = circumference of a circle which is equal to the total  length of two arcs of semicircles
      A = total area of a quarter mile race track
      
The total distance of a race in feet is equal to



The total distance of a race is




The total length of the two semicircles is equal to the circumference of a circle because the diameter of the two semicircles is the same which is d. The diameter of the two semicircles or the width of a rectangle is equal to






The total area of a quarter mile race is







The length of a race from S to D by way of C in feet is equal to








The length of a race from S to D by way of C in yards is equal to



 

Tuesday, April 22, 2014

Trapezoid, Quadrilateral Problems, 3

Category: Plane Geometry

"Published in Newark, California, USA"

Find the area of the rectilinear figure shown, if it is the difference between two isosceles trapezoids whose corresponding sides area parallel.

Photo by Math Principles in Everyday Life

Solution:

The given plane figure consists of the difference of two isosceles trapezoids. Let's analyze and label further the above figure as follows

Photo by Math Principles in Everyday Life

The area of a large trapezoid is





Before we solve for the area of a small trapezoid, we need to solve for the variables first.




Using Pythagorean Theorem







The height of a small trapezoid is



Since the given two trapezoids are isosceles trapezoid with the common thickness which is 2", then we can solve for the variables by using similar triangles. 

Using similar triangles




The length of the upper base of a small trapezoid is





Using similar triangles




The length of the lower base of a small trapezoid is





Hence, the area of a small trapezoid is





Therefore, the area of a plane figure is