t1 = 0 : 0.01 : 5-0.1;
t2 = 5 : 0.01 : 10-0.1;
t3 = 10 : 0.01 : 15-0.1;
t4 = 15 : 0.01 : 20-0.1;


x1 = cos(2*pi*7*t1);
x2 = 0.5* cos(2*pi*14*t2);
x3 = 2*cos(2*pi*21*t3);
x4 = 4*cos(2*pi*28*t4);

plot(t1,x1);hold on;
plot(t2,x2);hold on;
plot(t3,x3);hold on;
plot(t4,x4);hold on;

title('½Ã°£¿¡ µû¶ó ÁÖÆļö°¡ º¯ÇÏ´Â cosine ½ÅÈ£')
xlabel('time(s)')
ylabel('Amplitude')

plot(0:100/1024:100-100/1024,abs(fft(x1,1024))); hold on;
plot(0:100/1024:100-100/1024,abs(fft(x2,1024)),'r'); hold on;
plot(0:100/1024:100-100/1024,abs(fft(x3,1024)),'k'); hold on;
plot(0:100/1024:100-100/1024,abs(fft(x4,1024)),'g'); hold on;

title('À§ ±×¸² FFT')
xlabel('frequency(Hz)')
ylabel('Amplitude')