RC=0.1;

f= @(w) abs(1./(RC*w*i+1))
N=100;
w1=linspace(0,10,N);
y1= f(w1);
w2= linspace(10,100);
y2=f(w2);

loglog(w1,y1,'b',w2,y2,'r')
xlabel('Omega(rad/s)', 'Fontsize',16)
ylabel('Ao/Ai>0.7',('Ao/Ai')<0.7')
text(10,0.7, 'o','Fontsize',16)