Question

1) Show that cos A * cos B = 0.5 [cos(A+B) + cos(A-B)] . Some English is essential in
addition to the algebra. Note that cosine is an even function so that cos(A-B) = cos(BA).
2) A mixer has a local oscillator at 1157 kHz and a bandpass filter centred at 455 kHz.
What are the centre frequencies of signals which would cause output from the filter?
How is it that a radio receiver accepts only one channel of input signal?