eq1:3*x^4+2*x^2=7;
sbst:x^2=u;

subst(sbst,eq1);

eq2:subst(last(solve(sbst,x)),eq1);
eq3:solve(eq2,u);

subst(solve(sbst,u),eq3);

subst([a=b,b=c,c=d],[a+b+c+d]);

psubst([a=b,b=c,c=d],[a+b+c+d]);

eq4:f_res=1/(2*π*sqrt(L*C));

circuit1:[L=1e-3,C=100e-12]; 
circuit2:[L=10e-3,C=1e-12];

float(subst(circuit1,eq4));

float(subst(circuit2,eq4));
