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                 ARMATHS CLASSES

Allied angles:

Two angles are said to be allied when their sum or difference is either zero or a multiple of ${90}^o$

Rule for finding Trigonometric Ratio of ($\frac{n\pi }{2}+\theta$)

             To find this out we need to know 3 things.

             First is complimentary function, like complimentary function for sin is cos and vice versa, Complimentary of tan is cot and vice versa, Complimentary for sec is cosec and vice versa.

             Second is we need to know the sign of trigonometric functions in different quadrants. In first quadrant, all trigonometric functions are positive. In second quadrant only sin and cos are positive. In third quadrant only tan and cot are positive. In fourth quadrant only cos and sec are positive rest are negative.

             Thirdly you need to know in which quadrant does an angle lies. Draw 4 quadrants, find where the angle will lie, note the quadrant.

             Once you are clear with these 3 things, you are all set for finding the value of trigonometric Ratio of ($\frac{n\pi }{2}+\theta$)

Things to remember while applying allied angle formula Rules

1. n is the multiple of ${90}^o$or $\frac{\pi }{2}$ and prefer to keep angle  θ as acute
2. This rule is not valid if angle is not of the form $\frac{n\pi }{2}+\theta$