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**a causal system?? the biggest contradiction!**

Hey guys - can someone tell me why i get two contradicting asnwers...

i am asked to determine whether the following system is causal or not:

y[k+1] + 0.64y[k-1] = x[k] + 2x[k-1]

method 1:

put k = k-1 (delay the signal by one unit)

therefore , y[k] = -0.64y[k-2] +x[k-1] +2x[k-2]

it is cleary that this signal is casual because a present ouptut value is dependent on present and past input/output values.

method 2:

put k = k+1

therefore, 0.64y[k] = y[k+2] +x[k+1] +2x[k]

now the system is clearly not causal!!!! whys is this happening!!

i can't see any error in my maths. Also , shifting should not alter the signal characteristics!!!

please someone help!!!

calculating a tranfer function clearly shows the system IS causal-----so what is up with metho 2?????????/

thanks!!!