3х=1+1/3+3/5
3х=29/15
х=29/45
A1+19d=20
a1+14d=-1
5d=20-(-1)=21 d=21/5=4.2
Cos6x*cos5x-sin6x*sin5x=0
Cos(6x+5x)=0
Cos11x=0
11x=arccos0+2pk
11x=pi/2+2pk
x=pi/22+2pk/11
20 - 3х + 40 + 5у = 100
5у - 3х = 40
3х = 40 - 5у
20 - 40 + 5y + 40 + 5y = 100
20 + 10y = 100
10y = 80
y = 8
3x = 40 - 5*8
3x = 40 - 40
3x = 0
x = 0
Ответ: y = 8
x = 0