MATLAB: The answer is wrong ( SIMPLE TRIGONOMETRIC)

functiontrigonometric

My code is:
function onex(y)
cos(y)*cos(y)-sin(y)*sin(y)
end
When I insert y=pi/4 The result is:
>> onex(pi/4)
ans =
     2.2204e-16
Does anybody has any suggestions? Thank you in advance!

Best Answer

to try to get zero as you want, you may have to do it in degrees.
x= pi/4*180/pi;
cosd(x)*cosd(x)-sind(x)*sind(x)
will get you your 0. This is because pi is not exactly pi. http://www.mathworks.com/help/matlab/ref/pi.html
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