1) 2x+12,3=x
2x-x+12,3=0
x+12,3=0
x=0-12,3
x=-12,3
2)-3x=6 3/7
-3x=45/7
x=45/7 : (-3)
x=45/7 * (-1/3) сокращаем на 3
x=15/7*(-1/1)
x=-15/7
x=-2 1/7
3)
-10,8:6/11 - 12,5 * (2/9)²
1} -108/10 * 11/6 = -18/10 * 11/1= -9/5*11= - 99/5
2} 12,5=12 1/2 = 25/2
25/2 * 4/81= 25/1* 2/81= 50/81
3} -99/5 -50/81= -(99/5+ 50/405) = -( 99*81+5*50) /405 = -(8019+250)/405=
=-8269/405 = -20 169/405