Vpa Solve solving for B

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Benneth Perez
Benneth Perez 2021-10-24
编辑： Benneth Perez 2021-10-25
Hello,
This is a follow up question to this one. Previous Question
For some reason i was previously getting a different answer using vpasolve and vpa which now works and I get the right answers for solving for the Beta variable. I'm now using the code to solve B for when the values of M1=3 and theta2=15. When i do this i start getting results with imaginary answers.
The correct answer should be something like 32.24 but I'm getting:
beta =
84.4217 + 5.8932e-37i
M1 = 3;
P1 = 1;
theta2 = 15;
thetha3 = 20;
gamma = 1.4;
syms beta
tantheta = tand(theta2);
x = 2*cotd(beta)*((M1^2*((sind(beta))^2)-1));
y = M1^2*(gamma+cosd(2*beta))+2;
eqn = x/y;
result = solve(tantheta == eqn, beta);
beta = vpa(result)+180

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采纳的回答

Walter Roberson
Walter Roberson 2021-10-24
Ran in:
M1 = 3;
P1 = 1;
theta2 = 15;
thetha3 = 20;
gamma = 1.4;
syms beta
tantheta = tand(theta2);
x = 2*cotd(beta)*((M1^2*((sind(beta))^2)-1));
y = M1^2*(gamma+cosd(2*beta))+2;
eqn = x/y;
b0 = 1;
result = vpasolve(tantheta == eqn, beta, b0);
beta = vpa(result)+180
beta = 
212.24040018274467042158222540358
  1 个评论
Benneth Perez
Benneth Perez 2021-10-25
编辑：Benneth Perez 2021-10-25
Hello,
Thank you for the help the solution which im looking for is the first one, should be 32.26. 212 does look like a solution however is not the smallest solution(first solution).
Do you mind telling me whath B0 =1; is for ?
My guess is that this is a first guess for the solution computation?
Follow up: Wow! actually this works! Exactly what my code needed, all i needed to do was remove the 180 and it gives me the solution im looking for. Adding 180 gives me the 4 solution.
Thank you

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