how to learn trignometry ratios suggest smple method

Look at the following figure.

Here, ABC is a right-angled triangle such that angle B = 90°.

Let us represent perpendicular by P, base by B and hypotenuse by H.

Then simple method to learn the ratios is as follows:

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Here,  

Also, below given table represents the values of different trigonometric ratios at few specific angles.

You just learn the values for sin A and the you can calculate the rest on you own.

For example, if you write the values of sin A in reverse order in the table then you will get the values of cos A.

tan A can be calculated from the formula sin A/ cos A.

Remaining ones such as coesec A, sec A and cot A are just reciprocals of sin A, cos A and tan A respectively. 

Hope it helps.

Best wishes!