1) (4/5)*10=4*2=8
2) (3/4)*(3/4)=9/16 см кв
3) 3* (2 5/9)=3*23/9=23/3=7 2/3
4) (35/18)*(9/42)=(35/2):42=(5/2)/6=5/12
5) (2 1/6)*(5 1/7)=(13/6)*(36/7)=13*6/7=78/7
6)51 *(12/17) + (1/12)*16 + (5/17)*51 - (1/12)* 4=36+(4/3)+15-
1/3=51+1=52
Ответ: 52
x-y=4
x*x-y*y=80
y=4-x
x*x-4-x*4-x=80
x^2+x^2=64
2x^2=64
x^2=32
x=4√2
31;73;37;71;17;13;70;30