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Sin150=sin(π-30)=sin30=1/2
sin165=sin(π-15)=sin15=sin(45-30)=sin45*cos30-cos45*sin30=√2/2*√3/2-√2/2*1/2=
sin150+sin165=1/2+√2/2*√3/2-√2/2*1/2=(1+√6-√2)/2
Tgx*ctx*ctg2x=0
tan(x) cot(2x)=0
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