помогите решить 2,3,4 или хотя бы одно!!пожалуйста
4) ctga-ctg2a=1/sin2a.
ctga-ctg2a=cosa/sina-cos2a/sin2a=cosa/sina-(cos^2(a)-sin^2(a))/(2sina*cosa)=(2cos^2(a)-cos^2(a)+sin^2(a))/(2sina*cosa)=1/sin2a.
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4) ctga-ctg2a=1/sin2a.
ctga-ctg2a=cosa/sina-cos2a/sin2a=cosa/sina-(cos^2(a)-sin^2(a))/(2sina*cosa)=(2cos^2(a)-cos^2(a)+sin^2(a))/(2sina*cosa)=1/sin2a.