Х: 8=800*10
х:8= 8000
х= 8000* 8
х=64.000
64.000:8=800*10
8000=8000
х*8=800:10
х*8=80
х= 80:8
х= 10
10*8=800:10
80=80
700:х=7*100
700: х=700
х= 700:700
х= 1
700:1= 7*100
700=700
1)2*15=30(дм)-ширина
2)40-30=10(дм)-на <
3)(30+40)*2=140(дм)-переметр
Сosx=a
6a²+a-1=0
D=1+24=25
a1=(-1-5)/12=-1/2⇒cosx=-1/2⇒x=+-2π/3+2πn,n∈z
a2=(-1+5)/12=1/3⇒cosx=1/3⇒x=+-arccos1/3+2πk,k∈z
12:3ц3/5=10/3
10/3+2/3=12/3
12/3 :1ц1/2 =8/3
8/3-1ц1/3= 8/3-3/3-1/3= 4/3 =1ц1/3
25км=2500дм
.............................