why do I get the wrong angle

why do i keep getting a negatie value for angle

[Torsten]

Why did you delete your question ?

Answer 1

[David Hill]

Recommend avoiding using symbolics. Seeking numerical solution, use fzero.

mo=2.5;
y=1.4;
angle=10;
fun=@(a)((2*(1+((y-1)/2)*mo^2*(sind(a)).^2))./(((y+1)*mo^2*sind(a).*cosd(a))))-tand(a-angle);
A=fzero(fun,32);

[Sarah Alhabbas]

I appreciate your response.

However, the code should give the ouput answer as 32 so it should not be included in the code.

[David Hill]

You could also plot and see that there are two solutions between (0 - 90).

mo=2.5;
y=1.4;
angle=10;
fun=@(a)((2*(1+((y-1)/2)*mo^2*(sind(a)).^2))./(((y+1)*mo^2*sind(a).*cosd(a))))-tand(a-angle);
x=3:.1:87;
plot(x,fun(x));

[David Hill]

When you graph the function you see solutions should be around 30 and 80. fzero requires an initial guess. 32 is not an exact solution.

mo=2.5;
y=1.4;
angle=10;
fun=@(a)((2*(1+((y-1)/2)*mo^2*(sind(a)).^2))./(((y+1)*mo^2*sind(a).*cosd(a))))-tand(a-angle);
A=fzero(fun,30)

A = 31.8506

mo=2.5;
y=1.4;
angle=10;
fun=@(a)((2*(1+((y-1)/2)*mo^2*(sind(a)).^2))./(((y+1)*mo^2*sind(a).*cosd(a))))-tand(a-angle);
A=fzero(fun,80)

A = 85.5761