cot (2pi+x) = cot x
This is because after a complete revolution the values of all trigonometric ratios repeat themselves.
cos 390 = cos ( 360 + 30 )
= cos 30
also the ratio does not transform after repetition of integral values of pi that is pi and 2 pi.
but they do transform after non integral values of pi like pi/2 and 3pi/2.
cos (pi/2 + x) = -sin x (cos is negative in second quadrant ) ------ 1
cos (pi/2 - x) = sin x ------- 2
cos (pi - x) = - cos x -------3 ( both 1 and 3 lie in the same quadrant but notice the difference )
cos (pi + x) = - cos x
similarly this can be followed foe 3pi/2 and 2pi also.
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