Tg31П/6=tg(31pi/6-5pi)=tgpi/6=1/sqrt(3)
(2 TgП/6 - TgП/3): cosП/6=(2sqrt(3)-sqrt(3)/3)*2/sqrt(3)=4-2/3=10/3
Ctg13П/4=ctg(13pi/4-3pi)=ctgpi/4=1
cos19П/3=cos(19pi/3-6pi)=cospi/3=1/2
9m^2-48m+64+16m^2-64+100m=25m^2+52m
Https://ru-static.z-dn.net/files/d28/51b2c2b8954ab8d96aa386c53b05e514.jpg
7x^2-14x=0
x^2-2x=0
x(x-2)=0
x1=0
x2=2