I'm trying implement a IIR filter.I know the IIR filter come from that equation:

and i found that for high pass filter the coefficients are:

where fc = cut freq.

here my matlab code:

fs = 1000;
fc=0.3;
r=exp(-2*pi*fc);
a = [(1+r)/2 -(1+r)/2];
b= [1 -r];
n = 0:1/(fs):20;
n1 = 1024;
x1 = cos(0.3*2*pi.*n);
x2 = cos(0.8*2*pi.*n);
%plot(n,x1);
%hold on
%plot(n,x2);
%hold on
%plot(n,x1+x2);
%aux = fft((x1+x2),n1);
%aux = aux(1:n1/2);
%f = (0:n1/2-1)*(fs/n1);
%length(f)
%legend('x1[n]','x2[n]','x1+x2')
%plot(f,abs(aux));
%hold on

y = filter([0.5759 -0.5759],[1 -0.1518] , x1+x2);
plot(n,y,'r-',n,x2,'b--',n,x1,'g-.');
grid
%axis([0 100 -1.2 4]);
ylabel('Amplitude');
xlabel('Time index n');
legend('y[n]','x2[n]','x1[n]')

the commented parts are from FFT part of program and it's working well but the filter function isn't working. Help me plz and sorry about my english.