Question: How to solve non linear equations

Dear Sir
I am getting the solution lambda=−1.518022637,beta=0.5666679932,p=4.035629244

Does this solution maximizes my objective function Zv. Also I am not getting the solution for non negative values of  p, lambda and beta.Can you please help me to solve following non linear equations with maple 10.

Thanking you
Priyaasha
 
 
P1:=((p-v)*R*D*k0*(1-exp(-k1*beta))/(k1*(R-D))+D*lambda*(p+h/sigma+v)-R*si*(h/sigma+2*v)-K)/(T+lambda);
 
P2:=subs([T=beta+D*k0*(1-exp(-k1*beta)),si=(ln(1+D*(exp(sigma*lambda)-1)/R))/sigma],P1);
 
Zv:=subs([D=160000*p^(-4)],P2);
 
Zvdp:=diff(Zv,p):
 
Zvdl:=diff(Zv,lambda):
 
Zvdb:=diff(Zv,beta):
 
X1:=subs(R=1000,v=6.3,K=1000,h=1,sigma=0.2,k0=0.9,k1=0.1,Zvdp):
 
X2:=subs(R=1000,v=6.3,K=1000,h=1,sigma=0.2,k0=0.9,k1=0.1,Zvdl):
 
X3:=subs(R=1000,v=6.3,K=1000,h=1,sigma=0.2,k0=0.9,k1=0.1,Zvdb):
 
X4:=fsolve({X1,X2,X3},{p,lambda,beta});