x=linspace(-30,30,100);
y=pr03a_fce(x);
plot(x,y,x,0);

hold on
r1=fzero('pr03a_fce',-18);
r2=fzero('pr03a_fce',-14);
r3=fzero('pr03a_fce',-12);
r4=fzero('pr03a_fce',-9);
r5=fzero('pr03a_fce',-5);
r6=fzero('pr03a_fce',-2);
r7=fzero('pr03a_fce',2);
r8=fzero('pr03a_fce',5);
r9=fzero('pr03a_fce',8);
r10=fzero('pr03a_fce',11);
r11=fzero('pr03a_fce',14);
r12=fzero('pr03a_fce',19);
r13=fzero('pr03a_fce',18);

plot(r1,pr03a_fce(r1),'x',r2,pr03a_fce(r2),'x',r3,pr03a_fce(r3),'x',r4,pr03a_fce(r4),'x',r5,pr03a_fce(r5),'x',r6,pr03a_fce(r6),'x',r7,pr03a_fce(r7),'x',r8,pr03a_fce(r8),'x',r9,pr03a_fce(r9),'x',r10,pr03a_fce(r10),'x',r11,pr03a_fce(r11),'x',r12,pr03a_fce(r12),'x',r13,pr03a_fce(r13),'x');
hold off