Question #19655

1 Answer
Aug 29, 2015

If any angle, #A#, is drawn in standard position using a unit length hypotenuse triangle,
the angle #(-A)# has the same #x# coordinate and the same hypotenuse length and
#rarr cos(A) = cos(-A)#

Explanation:

For a triangle with unit length hypotenuse in standard position,
the #cos# of the angle at the origin is the #x# coordinate.

Since the #x# coordinate of #/_ A# is the same as the #x# coordinate of #/_-A#
#cos(A) = cos(-A)#

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