Trig Ratios

Concept

Suppose that we want to find the trig ratios of a trigonometry function ( sine, cosine, tangent ). We need to express the trig ratios in its simpliest form.

Trig Ratios of an angle can be found by the following steps:

1) Let us look at the quadrant in which is in. Here, is in the 2 nd quadrant.

2) We find the basic angle of . In this example, we have indicated it .

3) The trig ratio of angle is equal to the trig ratio of the basic angle numerically, the sign being determined by the ‘ASTC' diagram.

 

can be in degrees or radians.

Examples

Let us look at the following examples to increase our understanding of the trig ratios.

Express the trigonometric ratio of the following angles in terms of the same trig ratios of the corresponding basic angle:

a) sine

is in the 2 nd quadrant and the basic angle of is .The basic angle is measured as the acute angle which OP makes with the x-axis .

Since sine is positive in the 2nd quadrant as seen in the ‘ASTC' diagram, .Thus the trig ratio would be sine

Wasn't finding the trig ratios easy ? See more examples of trig ratios and try converting trig ratios yourself.

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