By the dual of the arguments of section 15.3 show that: a) The filter with impulse response is a causal filter whose frequency response for large T approximates that of an ideal low pass filter except...

By the dual of the arguments of section 15.3 show that:

a) The filter with impulse response

is a causal filter whose frequency response for large T approximates that of an ideal low pass filter except for finite "ears" at the edge of the band.

b) The filter with impUlse response

is a causal filter approximating an ideal low pass filter for large T without the "ears " of the impulse response of (a).