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(1.,8)
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(1-tg2x tgx) (1+tg2x tgx) =?
числитель = 1 - tg2x tgx = 1 - Sin2x/Cox2x * Sinx/Cosx =
= (Cos2xCosx -Sin2xSinx)/(Cos2xCosx) = Cos(2x+x) /(Cos2xCosx) =
=Cos3x/(Cos2xCosx)
знаменатель = 1 + tg2x tgx = 1 + Sin2x/Cox2x * Sinx/Cosx =
= (Cos2xCosx + Sin2xSinx)/(Cos2xCosx) = Cos(2x-x) /(Cos2xCosx) =
=Cosx/(Cos2xCosx) = 1/Cos2x
Теперь сама дробь =
= Cos3x/(Cos2xCosx) : 1/Cos2x = Cos3x/Cosx
Если 2400/5=480 т.е. 1/5=480 2/5 =960 тогда 2400-960=1440
Сosa=4/5
sina=+-√(1-cos²a)=+-√(1-16/25)=+-√(9/25)=+-3/5
tga=sina/cosa
tga=+-3/5:4/5=+-3/5*5/4=+-3/4