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how to solve equation to find angle

조회 수: 2 (최근 30일)
Megha
Megha 2020년 8월 29일
댓글: VBBV 2020년 9월 8일
I have the values of variables be like:
clear;
Vau = 43.0;
Vsu = 47.45;
beta = 1.41;
gamma = 5/3;
syms theta_u
I wish to find the value of theta_u.
For this, I have an equation like
when i solved this equation it turns out to be like
Now I put this equation for solving it to matlab using code:
Q3 = double(solve(Vsu*(cosd(theta_u*(sqrt(2/(beta*gamma)))))*(1/(Vau*(cosd(theta_u))))-1))
it gives an error
Q3 = double(solve(Vsu*(cosd(theta_u*(sqrt(2/(beta*gamma)))))*(1/(Vau*(cosd(theta_u))))-1))
Warning: Unable to solve symbolically. Returning a numeric approximation instead.
> In solve (line 304)
Q3 =
-162.2052
which is also a wrong answer. The correct answer is 71.8. Please suggest if there are any corrections.
  댓글 수: 2
Alan Stevens
Alan Stevens 2020년 8월 29일
Using fzero, I also get either 162.2052 or -162.2052 (depending on the initial guess). Why do you think the answer should be 71.8? Have you doube checked your equation and constants?
VBBV
VBBV 2020년 9월 8일
Place the term in sqrt outside the cost parenthesis
Try this
Q3 = solve(sqrt((beta*gamma)/2)*acos((sin(theta_u)*Vau)/Vsu),theta_u)
You will get two values ...
Q3 =
asin(949/860)
pi - asin(949/860)
Multply the first real(asin(949/860)*180/pi)
To get 90 deg

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