we get repeatative values of sin , cos and tan etc after 360 degree. so if at 90 degree, some value is changes from say cos to sin then it will be repeatative after every 360 degree. now see the graph. sin and cos are identical only there is phase difference of 90 degree. graph is exactly same if x- axis is moves by 90 degree. similarly other value u say are also interchangable. this is graph proof.
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Videonotes.in Gmail Is Email I... answered this
see the image. angle abc=90, so sum of angle bca and cab=90 degree. sin theta= p/h, cos theta = b/h.
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Videonotes.in Gmail Is Email I... answered this
ignore this image above proof is enough..it's too complicated..forget it. sorry for this image.
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Mohammed Abdulla answered this
Because it lies in the Y-co ordinate and 0 and 360 degrees lie in the x-co ordinate