Help in solving non-linear equation

Question

ana take 2017-1-16

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https://ww2.mathworks.cn/matlabcentral/answers/320617-help-in-solving-non-linear-equation

回答： Star Strider 2017-1-16

I tried this command to solve the equation inside the brackets: solve('sqrt(((4 + 0.1*cos((PI/6)*t)) - ( 3 + 0.1*sin(cos((PI/3)*t))))^ 2+ ((9 + 0.1*sin((PI/6)*t)) - (6 + 0.1*sin((PI/3)*t)))^ 2)-4 = 0') Warning: Support of character vectors that are not valid variable names or define a number will be removed in a future release. To create symbolic expressions, first create symbolic variables and then use operations on them. > In sym>convertExpression (line 1559) In sym>convertChar (line 1464) In sym>tomupad (line 1216) In sym (line 179) In solve>getEqns (line 405) In solve (line 225) Warning: Do not specify equations and variables as character vectors. Instead, create symbolic variables with syms. > In solve>getEqns (line 445) In solve (line 225)

ans =

Empty sym: 0-by-1

What does this mean?Can anyone help to solve this equation?

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Answer 1

Star Strider 2017-1-16

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https://ww2.mathworks.cn/matlabcentral/answers/320617-help-in-solving-non-linear-equation#answer_250779

在 MATLAB Online 中打开

There is no solution, since your function never crosses zero.

Run this to understand your problem:

syms t 
f = symfun(sqrt(((4 + 0.1*cos((pi/6)*t)) - ( 3 + 0.1*sin(cos((pi/3)*t))))^ 2+ ((9 + 0.1*sin((pi/6)*t)) - (6 + 0.1*sin((pi/3)*t)))^ 2)-4, t);
figure(1)
fplot(f, [-50, 50])
axis([xlim    -1.5  0.5])
grid