Cos²a=1:(1+tg²a)=1:(1+1/4)=4/5
cosa=2/√5
sina=√(1-cos²a)=√*1-1/5)=1/√5
cos2a=cos²a-sin²a=4/5-1/5=3/5
sin2a=2sinacosa=2*1/√5*2/√5=4/5
(sin2a-cos2a)/(sin2a+cos2a)=(4/5-3/5)/(4/5+3/5)=1/5*5/7=1/7
Формула n-члена арифметической прогрессии:
![a_{n}](https://tex.z-dn.net/?f=+a_%7Bn%7D+)
=
![a_{1}](https://tex.z-dn.net/?f=+a_%7B1%7D+)
+(n-1)*d
d=-6-(-3)=-6+3=-3.
![a_{1}](https://tex.z-dn.net/?f=+a_%7B1%7D+)
=-3
![a_{25}](https://tex.z-dn.net/?f=+a_%7B25%7D+)
=-3+(25-1)*(-3)=-3+24*(-3)=-3-72=-75
ОТВЕТ: -75
(∛(16+260)/∛13)/√√16=(∛276/∛13)/2........................................
Ctg²(β+π/2)-cos²(β-π/2)/ctg²(β-π/2) -cos²(β+π/2)=
=(-tgβ)² -sin²β/(-tgβ)² -(sinβ)²=
=tg²β-cos²β-sin²β=tg²β-1;