MATLAB计算无法获得数值解

[mashuai9633]

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计算这个方程，其中a0=15°，k=0.000422，q=0.04，Fa=22，Z=17，Db=6.85；
我编写的MATLAB程序如下
a0=15*pi/180;
k=0.000422;
q=0.04;
Fa=22;
Z=17;
Db=6.85;
b=(k/q)*(Fa/(Z*Db))^(2/3);
a=solve('(cos(a0)/cos(a*pi/180)-1)*(sin(a*pi/180))^(2/3)=b','a')
结果是
b =

0.0035


a =

(Dom::ImageSet(-(180*(acos(z1) + 2*pi*k))/pi, [k, z1], [Z_, RootOf(z^5 - 3*z^4*cos(a0) - z^3*(- 3*cos(a0)^2 + b^3 + 1) + z^2*(3*cos(a0) - cos(a0)^3) - 3*z*cos(a0)^2 + cos(a0)^3, z)]) intersect (Dom::ImageSet((180*(asinh(x)*i + 2*pi*k))/pi, [k, x], [Z_, Dom::Interval(0, Inf)]) union Dom::ImageSet(180*k, k, Z_) union Dom::ImageSet((180*(pi - asin(x*i + y) + 2*pi*k))/pi, [k, x, y], [Z_, R_, Dom::Interval(0, Inf)]) union Dom::ImageSet(-(180*(pi + asinh(x)*i + 2*pi*k))/pi, [k, x], [Z_, Dom::Interval(0, Inf)]) union Dom::ImageSet((180*(asin(x*i + y) + 2*pi*k))/pi, [k, x, y], [Z_, R_, Dom::Interval(0, Inf)])) union Dom::ImageSet((180*(acos(z1) + 2*pi*k))/pi, [k, z1], [Z_, RootOf(z^5 - 3*z^4*cos(a0) - z^3*(- 3*cos(a0)^2 + b^3 + 1) + z^2*(3*cos(a0) - cos(a0)^3) - 3*z*cos(a0)^2 + cos(a0)^3, z)]) intersect (Dom::ImageSet((180*(asinh(x)*i + 2*pi*k))/pi, [k, x], [Z_, Dom::Interval(0, Inf)]) union Dom::ImageSet(180*k, k, Z_) union Dom::ImageSet((180*(pi - asin(x*i + y) + 2*pi*k))/pi, [k, x, y], [Z_, R_, Dom::Interval(0, Inf)]) union Dom::ImageSet(-(180*(pi + asinh(x)*i + 2*pi*k))/pi, [k, x], [Z_, Dom::Interval(0, Inf)]) union Dom::ImageSet((180*(asin(x*i + y) + 2*pi*k))/pi, [k, x, y], [Z_, R_, Dom::Interval(0, Inf)]))) minus (Dom::ImageSet(-(180*(a0 + 2*pi*k))/pi, k, Z_) union Dom::ImageSet((180*(a0 + 2*pi*k))/pi, k, Z_) union Dom::ImageSet(180*k + 90, k, Z_))
我想要的是a的数值解，但是现在的结果确实这样的，如何解决这个问题。