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diff --git a/40/CH8/EX8.24/Exa_8_24.sce b/40/CH8/EX8.24/Exa_8_24.sce
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+//The importance of Periodic extension
+//(a)For M=3
+x=[1 2 1];
+XDFT=dft(x,-1)
+w=exp(-%i*2*%pi/3);
+for i=1:3
+    for j=1:3
+        WN(i,j)=w^((i-1)*(j-1));
+    end
+end
+WI=WN';
+xn=1/3*WI*XDFT
+//The result is periodic with M=3 & 1 period equals x[n]
+//(b)For M=4
+y=[1 2 1 0];
+YDFT=dft(y,-1)
+w=exp(-%i*%pi/2);
+for i=1:4
+    for j=1:4
+        WN(i,j)=w^((i-1)*(j-1));
+    end
+end
+WI=WN';
+yn=1/4*WI*YDFT