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Start with a simple baseband tone Take m ( t ) = cos ( ω m t ) m(t)=\cos(\omega_m t) and carrier cos ( ω c t ) . \cos(\omega_c t). If we simply multiply them: s ( t ) = m ( t ) cos ( ω c t ) s(t)=m(t)\cos(\omega_ct) then s ( t ) = cos ( ω m t ) cos ( ω c t ) . s(t)=\cos(\omega_mt)\cos(\omega_ct). Using cos A cos B = 1 2 [ cos ( A + B ) + cos ( A − B ) ] , \cos A\cos B =\frac12[\cos(A+B)+\cos(A-B)], we get s ( t ) = 1 2 cos ( ( ω c + ω m ) t ) + 1 2 cos ( ( ω c − ω m ) t ) \boxed{s(t)=\frac12\cos((\omega_c+\omega_m)t)+\frac12\cos((\omega_c-\omega_m)t)} So we get two frequencies : ω c + ω m \boxed{\omega_c+\omega_m} and ω c − ω m . \boxed{\omega_c-\omega_m}. These are the upper sideband (USB) and lower sideband (LSB) . We want only one Suppose we want the upper side...