Wrong final answer using symbolic equations

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Diana Dawoud 2022-1-7

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https://ww2.mathworks.cn/matlabcentral/answers/1624110-wrong-final-answer-using-symbolic-equations

评论： David Goodmanson 2022-1-7

I'm trying to write this simple code, the right answer is 0.3 with an angle of 143.13, the answer that I'm getting is 0.5 with an angle of 90.76, any reason why I'm getting the wrong answer

syms C w R
V=150*exp(1i*pi/2)
Xc= 1/(1i*w*C)
Z=R+Xc
z=subs(Z,[C w R],[0.25*10^(-6) 10^4 300])
I=V./z

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David Goodmanson 2022-1-7

在 MATLAB Online 中打开

Hello Diana,

I ran the code, followed by

Im = double(abs(I))
Ia = double(angled(I))

and got the answer you were expecting. Hard to say what might have gone wrong.

By the way for a problem like this there is no need to use symbolic variables, only to immediately substitute in values. It's easier to not bother and start out with C = 0.25*10^(-6), w = 10^4 etc.

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