[tex] \cos( - 7.9\pi)tg( - 1.1\pi) - \sin5.6\pi \: ctg4.4\pi[/tex]​

[tex]cos(-7,9\pi)tg(-1,1\pi)-sin5,6\pi ctg4,4\pi=cos(8\pi-\frac{\pi }{10})*(-tg(\pi+\frac{\pi }{10}))-sin(6\pi-\frac{2\pi }{5})*ctg(4\pi+\frac{2\pi }{5})=-cos\frac{\pi }{10}tg\frac{\pi }{10}+sin\frac{2\pi }{5}*ctg\frac{2\pi }{5}=-sin\frac{\pi }{10}+cos\frac{2\pi }{5}[/tex]

pusti budet x i y storoni

{x+y=31

x*y=210,

{x=31-y

(31-y)y=210

31y-y2=210

-y2+31y-210=0

d=31^2-4*210=121

y1=10

y2=21

znachit odna storona rovna 10 a vtaraja naidem:

x+10=31

x=21

otvet: 10 i 21

по формуле получаем:

cos (5x+7x) = √3/2

cos 12x =  √3/2

12x =  ±π/6 + 2πk, где k∈z

x=±π/72 +  πk/6, где k∈z

ответ:   ±π/72 +  πk/6, где k∈z