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Learn Trigonometry : Help in Easily Learning Simple Trig Math (with rhyme to remember)

Updated on March 19, 2013

Trigonometry formulas table

sin Θ
cos Θ
tan Θ
Opposite (O)
Base (B)
Opposite (O)
Hypotenuse (B)
Hypotenuse (B)
Base (B)
Table 1

Trigonometry is a part of advanced mathematics. It's actually the foundation of advanced mathematics. The word 'trigonometry' is formed by two Greek words 'trigonon' which means triangle and 'metria' which means action or process of measuring. So the most essential application of trigonometry is to measure the sides of a triangle. This article won't discuss the details of trigonometry. We'll just take a look at the basic formulae involved in the calculation of trigonometric values.

Consider the image shown above. It's a right angled triangle ΔABC. The three sides AB, BC and AC are the Hypotenuse, Opposite side and Base respectively. It's with respect to the angle between the two sides AB and AC. We can call it Θ. Angle ACB is a right angle. The lengths of the three sides are as follows:




If you observe carefully, all the lengths have been denoted by the small letter of the Vertex they are opposite to. That's the standard practise.

The sine, cosine and tangent of the triangle are calculated as follows:

sin Θ = Opposite/Hypotenuse = a/c

cos Θ = Base/Hypotenuse = b/c

tan Θ = Opposite/Base = a/b

From the above equations you can easily deduce:

tan Θ = sin Θ/cos Θ

Would you like to learn a simple method of remembering these formulas? Then do as follows:

  • First denote Opposite side by O, Hypotenuse by H and Base side by B.
  • Then draw a table as shown in Table 1.
  • The column header in the table corresponds to the values which are being calculated which are sine, cosine and tangent.
  • The 2nd row is of the numerator values and the 3rd row is of the denominator values.
  • The letters inside the bracket are of the assumptions which we have made.
  • Memorize the table as it is.
  • Read the letters in the bracket from the first column, then the second, followed by the third column.
  • The sequence is O H B H O B
  • Now we can create a rhyme which we can remember easily and recall it later on when we need them to do some trigonometric calculations.
  • One such rhyme can be : "Oscar Brought His Orange Bat". This is just an example. You can build upon it.

This article is Part 1 of the series of articles related to Learning Trigonometry. Read the other part/s for more information.


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