# How calculate tangent to -1 of cos (1/4) without pythagoras

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Supposing that the problem provides the measure of angle in degrees, hence `cos (1/4)^o = 0.999.`

You need to evaluate the inverse of trigonometric function tangent such that:

`tan^(-1)(cos(1/4)^o) = tan^(-1)(0.999)`

Using the calculator of inverse trigonometric functions yields:

`tan^(-1)(cos(1/4)^o) = 44.971^o + n*pi`

**Hence, evaluating the inverse of trigonometric function tangent yields `tan^(-1)(cos(1/4)^o) = 44.971^o + n*pi.` **

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