6) 2sin5α*cos3α-sin8α=
2sin5α*cos3α-sin(5α+3α)=
= 2sin5α*cos3α-( sin5α*cos3α+cos5α*sin3α )=
=2sin5α*cos3α- sin5α*cos3α-cos5α*sin3α =
=sin5α*cos3α -cos5α*sin3α =
=sin(5α-3α)=sin2α
