Тригонометрические функции.

Question

Тригонометрические функции.

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Answer 1

1) (sin20-sin40)/(1-cos20+cos40)=(sin20-2sin20*cos20)/(1+cos40-cos20)=sin20*(1-2cos20)/(2(cos20)^2-cos20)=sin20(1-2cos20)/cos20(2cos20-1)=-tg20

2)  (sin25*cos5-cos25*sin5)/(cos15*cos5-sin15*sin5)=sin(25-5)/cos(15+5)=sin20/cos20=tg20
3)   -tg20<tg20