5. * * * sin(α+β) = sinα *cosβ+cosα*sinβ * * *
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a) sin(x+3x) >1/2 ;
sin4x >1/2 ;
2πn + π/6< 4x < π-π/6</strong> +2πn , n∈Z ;
π/24 + πn/2
x∈ (π/24 + πn/2 ; 5 π/24+πn/2) , n∈Z .
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б) sin(2x+5x) > -√3/2 ;
sin7x > -√3/2 ;
2πn -π/3 < 7x < π+π/3</strong> +2πn , n∈Z ;
-π/21+2πn/7 < x < 4π/21+<strong> 2πn/7, n∈Z .