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Real-valued and causal FIR filters have a (generalized) linear phase response if and only if their coefficients satisfy either
$$h[n]=h[N-1-n]\tag{1}$$
or
$$h[n]=-h[N-1-n]\tag{2}$$
where $N$ is the filter length (number of taps).
There are four types of linear phase FIR filters, depending on the type of symmetry (even as in $(1)$ or odd as in $(2)$), ...
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