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Friday, January 25, 2013

More Integration Procedures

Category: Integral Calculus, Trigonometry

"Published in Newark, California, USA"

Evaluate

Solution:

Since there's a double angle involved in the integration, we have to convert it into it's equivalent single angle as follows

















Consider











Consider









Consider











Therefore










Thursday, January 24, 2013

Right Circular Cylinder - Cube

Category: Solid Geometry

"Published in Newark, California, USA"

Find the volume and total area of the largest cube of wood that can be cut from a log of circular cross section whose radius is 12.7 in.


Photo by Math Principles in Everyday Life

Solution:

Since the radius of a wood log is given, we have to consider the cross section of a wood log as follows


Photo by Math Principles in Everyday Life

As you notice that a square is inscribed in a circle. There are 6 equal squares in a cube and so all the sides of a cube are equal. The radius of a wood log or a circle is equal to ½ of its diagonal. The diagonals of a square bisect each other at a right angle. A right triangle that has two equal sides and two equal angles is called an isosceles right triangle. In this figure, there are four isosceles right triangles in a square. By Pythagorean Theorem,













The length of a side of a cube is 17.9605 in.

The total area of a cube is







The volume of a cube is 








Wednesday, January 23, 2013

Approximate Value - Cube Root

Category: Differential Calculus, Arithmetic

"Published in Newark, California, USA"

Find the approximate value of ∛200 without using a calculator.

Solution:

Well, we know that

             13 = 1

             23 = 8

             33 = 27

             43 = 64

             53 = 125

             63 = 216       and so on.

Since 200 is between 125 and 216, the 200  is between 5 and 6. We can get the approximate value of 200  without using a calculator as follows

Let
then

If   x = 216 (please choose this number because it is close to 200)
   dx = 200 - 216 = -16

then dy will be







Therefore









using a calculator



and using a scientific calculator



which is close to the final answer.