X-y=9
X=9+y
2 (9+y)+y=21==>18+2y+y=21==>3y=21-18==>3y=3=>>y=1 y=1
2x+y=21
2x+1=21
2x=20
x=20/2=10
x+y=10+1=11
2л-3кот; 4л-?кот, решение (4*3)/2=6 котелков
(56b+24):4=56b:4+24:4=14b+6
А) -х =5 1/3;
x=-5 1/3
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б) -х = - 3,2;
x=3,2
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в) -(-х )= - 0,5;
x=-0,5
========
г) - (-х) =10.
x=10
1) 8 9/10 - 3 3/10 = (89 - 33) / 10 = 56/10 = 5 6/10 (=5,6)
2) 1 - 1/7 = 7/7 -1/7= (7-1)/7 = 6/7
3) 1 - 1/15 = 15/15 - 1/15 = (15-1)/15 = 14/15
4) 1 - 1/12 = 12/12 - 1/12 = 11/12
5) 1 - 2/9 = 9/9 - 2/9 = 7/9