Крест на крест
7n=3*21
7n=63
n=63:7=9
13n=39*8
n=39*8:13= 24
30n=48*5
n=48*5:30=8
7n=9*49
n=9*49:7=63
D=<span>(2t+4)^2+4t<0
4t^2+20t+16<0
t^2+5t+4<0
</span>t^2+5t+4=0
t1=-1
t2=-4
t ∈ (- 4; -1)
4cos^2(x)-7Sin(2x)=2(Cos^2(x)+sin^2(x))
2Cos^2(x)-2Sin^2(x)-7Sin(2x)=0
2Cos(2x)-7Sin(2x)=0
tg2x=2/7
2x=arctg(2/7)+pn
x=1/2arctg(2/7)+pn/2
Х+у=-3 | 3
3х+3у= -9
(3х+3у)+(-3х+3у)=-18
6у=-18
у=- 18:6
у=-3
х+у=-3
х=3+(-3)
х=0