Giúp mk vs ạ 1) 4sin x/2+6cos x/2=(1÷2cos^2 x/4-1)-5sin^2(x+x/2) 2) 3sin^2(2π-x)-2sin(x+π/2).cos(x+5π/2)=0 3) 2(sin^4x+cos^4x)/cos2x +√3sin2x=1/cos2x

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