# Symbolic element to equation for differentiation

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Commented: Steven Lord on 10 Oct 2022
Dear all,
I am trying to solve some differential equations in MATLAB and trying to solve them for x and z. But I just get the equations being printed rather than the output being solved.
a = 0.8
syms x z
x = @(x,z)((((1-(a^2))^0.5)*(((x)/(z))+((z)/(x)))*(a-1+((1-((z)/(x)))^2.25)))^-1);
dxz = diff(x,z);
syms x z
ABD = ((x)*(z)/2) + (((x)/4)*(((x)*(x)/(z)) + (z))) - ((1/8)*((((x)*(x)/(z))+ (z))^2)*asin((2*(x)*(z))/(((x)*(x)) + ((z)*(z)))));
pdBDx = diff(ABD,x);
pdBDz = diff(ABD,z);
DiffAABD = (1/2) + ((pdBDx*dxz)+pdBDz)*((1-(a^2))^0.5);
muABD = a*(1/((1-(a^2))^0.5)) * (1/(((x*x/z*z)+1)*z/2))* 0.5;
dybydt = DiffAABD/muABD
I would like to at the end have dybydt(1,1), but when I do it the output is
ans =
(4*z*(x^2 + 1)*((2*x)/5 - (x*(x^2/z^2 - 1))/5 + (4*(((4*x)/(5*z^2) - 4/(5*x))/(((4*x)/(5*z) + (4*z)/(5*x))^2*((1 - z/x)^(9/4) - 2/5)) + (9*(1 - z/x)^(5/4))/(4*x*((4*x)/(5*z) + (4*z)/(5*x))*((1 - z/x)^(9/4) - 2/5)^2))*((3*z)/4 + (3*x^2)/(4*z) - (((2*z)/(x^2 + z^2) - (4*x^2*z)/(x^2 + z^2)^2)*(x^2/z + z)^2)/(8*(1 - (4*x^2*z^2)/(x^2 + z^2)^2)^(1/2)) - (x*asin((2*x*z)/(x^2 + z^2))*(x^2/z + z))/(2*z)))/5 - (((2*x)/(x^2 + z^2) - (4*x*z^2)/(x^2 + z^2)^2)*(x^2/z + z)^2)/(10*(1 - (4*x^2*z^2)/(x^2 + z^2)^2)^(1/2)) + (asin((2*x*z)/(x^2 + z^2))*(x^2/z^2 - 1)*(x^2/z + z))/5 + 1/2))/3
I want them solved for x and z. I had also tried dybydt = @(x,z)DiffAABD/muABD also additing @(x,z) to all the equationsbut doesn't work. Your answers would be really helpful, thanks. :)
Steven Lord on 10 Oct 2022
The equation for x would ideally be x ...
No, that is your implementation. Please show us the mathematical equation you're trying to solve (equations not code.) You can use the equation editor (the Sigma sign in the Insert section of the toolstrip of the comment box) to enter it, or you could attach an image of the equation if it's from a book or paper.

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