x+y+z=42 6t+7t+8t=42
p=42 21t=42 t=2 x=6*2=12 a=12/2=6
y=7*2=14 b=14/2=7
z=8*2= 16 c=16/2=8
=9х(2)+ху-81ху-9у(2)+80ху=9х(2)-9у(2)
= 5р(2)q-(5p(2)+5p(2)q-q -q(2))= 5р(2)q-5p(2)-5p(2)q+q+q(2)=-5p(2)+q+q(2)=q(2)+q-5p(2).
1) cos5α-cosα = -2sin2α*sin3α ;
2) cosα - cos3α +2sin2α = 2sinα *sin2α +2sin2α =2sin2α*(sinα+1) =
2sin2α(1 +cos(π/2 -α)) =4sin2α*cos² (π/4 - α/2).
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cosα - cos3α +2sin2α = 2sinα *sin2α +2sin2α =2sin2α*(sinα+1) =
2sin2α(sinα+sinπ/2) =4sin2α*sin(π/4 +α/2)*cos(π/4 -α/2) =
[[ но *** sin(π/4 +α/2) =cos(π/2 -(π/4 +α/2)) =cos(π/4 - α/2) *** ]] =
4sin2α*cos² (π/4 - α/2).