kill(all)$globalsolve:true$

RR:[
F*cos(α)-N_1+N_2*1/2+N_3*1/2=0,
F*sin(α)-N_2*sqrt(3)/2+N_3*sqrt(3)/2=0
];

FR:[
Δ_1=N_1*l/ES,
Δ_2=N_2*l/ES,
Δ_3=N_3*l/ES
];

DP:[
Δ_1=u,
Δ_2=-u*1/2+v*sqrt(3)/2,
Δ_3=-u*1/2-v*sqrt(3)/2
];

linsolve(append(RR,FR,DP),[N_1,N_2,N_3,Δ_1,Δ_2,Δ_3,u,v]);