1+cos7x=(sin1,5x-cos1,5x)^2
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1+cos7x=(sin1,5x-cos1,5x)^2 1+cos7x=sin²(1.5x)-2sin(1.5x)cos(1.5x)+cos²(1.5x)cos7x=-sin3xcos7x=cos(3x+π/2)3x+π/2=±arccos(cos7x)+2πn3x+π/2=±7x+2πnx(3±7)=-π/2+2πnx=(-π/2+2πn)/(3±7), n∈ZОтвет:x=(-π/2+2πn)/10x=-(-π/2+2πn)/4n∈Z