Trigonometric Ratio

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Trigonometric Ratio

The CAST rule

C Quadrant

cosθ and secθ will be positive

A Quadrant

All trigonometric ratios and their corresponding reciprocal functions are positive.

T Quadrant

tanθ and cotθ will be positive

S Quadrant

sinθ and cscθ will be positive.

The special triangles

How to sketch an angle

Terminal Arm: the ray the defines the end of the angle

Initial Arm: the ray that defines the beginning of the angle.

An example

tan(11π/6)= -tan(π/6)= -1/√3

sec (5π/4) = -sec(π/4)= -√2