how to use @ to solve math problems?

I can't recall on how to use @x in solving an algebraic problem. It has been a while for me using matlab to solve math problems for me?

Can someone please help resolve this?

mp = .211; % mass of piston [kg];
syms d
y = l+a-(sqrt((l^2)-(a^2)*(sind(d))^2)+a*cosd(d)); 
ap = diff(y,2); % acceleration of piston [m/s^2];
phi = asind((a*sind(d))/l);
Fcr = T/(a*cosd(d+phi)); % Force of connecting rod [N];

%a);
Ffr_1 = @(180) - Fcr*cosd(180)-mp*ap

[VBBV]

Ffr_1 = solve(@(d) Fcr*cosd(180)*(pi/180)-mp*ap,d)

[Walter Roberson]

Or

Ffr_1 = vpasolve(Fcr*cosd(180)*(pi/180)-mp*ap, d)