How to learn six basic trigonometric ratios sin, cos, tan, cot, cosec and sec?

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Six Trigonometric Ratios (sin, cos, tan, cot, sec and cosec)

June 15, 2017 by admin 1 Comment

Trigonometric Ratios (sin, cos, tan, cot, sec and cosec)

These six trigonometric ratios form the base of trigonometry. So, learn them carefully. Lets suppose we have triangle ABC right angled at B. We have angle

$\theta$

and

$\alpha$

$\triangle ABC$

Note that opposite side of angle

$\theta$

is AB and opposite side of angle

$\alpha$

is BC.

Adjacent side to angle

$\theta$

is BC and adjacent side to angle

$\alpha$

is AB.

AC is the hypotenuse of triangle ABC.

Now you have to memorize this sentence “Old Harry And His Old Aunt”. Don’t worry it is not an English class. It will help you to memorize formulas of six trigonometric ratios which are sin, cos, tan, sec, cosec and cot. Now look at all the capital letters of the sentence which are O, H, A, H, O and A. Now suppose that O stands for opposite side, H for hypotenuse and A for adjacent side. First two capital letters form sin, next two form cos and last two form tan. Confused? 🙁 Don’t worry it will be clear with the following.

$sin \theta=\frac{O}{H}=\frac{opposide side}{hypotenuse}=\frac{AB}{AC}$