<span>3070+С*8-2100=1370
8С+970=1370
8С=1370-970
8С=400
С=50
</span>
980+В*65+7800=8910
65В+8780=8910
65В=8910-8780
65В=130
В=2
<span>2200:a-(149+651)=300<u>
</u>2200:а-<u />800=300
2200:а=300+800
2200:а=1100
а=2200:1100
а=2
<u /></span>
1)7x=714
X=714÷7
X=102
И получаем 6х-612,8х-816,7х-714
x=9 или x=-3
(x-3)²=36 x²-6x+9=36