MATLAB: The result of acosd (0) only 90

cosd acosd

Why the result of acosd (0) only 90? In mathematics it should be 90 and 270. Can anybody explain to me why the matlab output is only 90? Thx b4 for the help
>> acosd(0)
ans =
    90

Best Answer

ACOSD is a SISO function that returns only one output value for each input value (real or complex).
You could see the behaviour of acosd in real, imaginary, absolute and phase plane.
x = [-5:0.00001:5];
subplot(2,2,1), plot(x,real(acosd(x)));
title('y = real(acos(\alpha))'),xlabel('\alpha [º]'),ylabel('y'),
subplot(2,2,2), plot(x,imag(acosd(x)));
title('y = imag(acos(\alpha))'),xlabel('\alpha [º]'),ylabel('y'),
subplot(2,2,3), plot(x,abs(acosd(x)));
title('y = abs(acos(\alpha))'),xlabel('\alpha [º]'),ylabel('y'),
subplot(2,2,4), plot(x,phase(acosd(x)));
title('y = phase(acos(\alpha))'),xlabel('\alpha [º]'),ylabel('y'),
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