-3.7•(2.5х-7.6)=-3.66+2.1х

A = {3; 1; -1}, |a| = √11
b = {2; 2; 1}, |b| = 3

cosφ = |3×2 + 1×2 + (-1)×1|/(3√11) = 7/(3√11) = (7√11)/33

Ответ: (7√11)/33

X+2/3=7/8
x+16/24=21/24
x=21/24-16/24
x=5/24
x-3/8=1/4
x-3/8=2/8
x=3/8+2/8
x=5/8
y-5/12=3/10
y-25/60=18/60
y=18/60+25/60
y=43/60
4/15+y=11/25
20/75+y=33/75
y=33/75-20/75
y=13/75

5*2+7*2+8*2=40см * це знак множення