3х-7800=1200
3х=9000
х=3000
Решение:
-2(5-3х)=7х+3
-10+6х=7х+3
6х-7х=3+10
-х=13
х=13/-1=-13
Ответ: х=-13
1/6 1/2 =1/6 3/6 1/9 и 1/3 = 1/9 и 3/9
3/10 и 2/5 = 3/10 и 4/10 5/9 и 7/18 = 10/18 и 7/18 9/14 и 6/7 = 9/14 и 12/14
1/5 и 7/25 = 5/25 и 7/25 1/2 и 1/6 и 2/3 = 3/6 и 1/6 и 4/6
1/4 и 5/7 и 9/28= 7/28 и 20/28 и 9/28 1/5 и 11/20 и 3/10= 4/20 и 11/20 и 6/20