Объяснение:
1) 9,5+8,9/2,3=18,4/2,3=8.
2) 12^4/3^3 × 2^6=20736/27×64=20736/1728=12
3) (2целых 1/9 - 3 целых 1/6):19/36 = (19/9 - 19/6):19/36 = (38-57/18):19/36 = -19/18:19/36 = -19/18 × 36/19 = -1/2.
4) √20 × √1,8 = √20×1,8 = √36 = 6.
5) 1/ 1/36+1/45 = 1/ 5+4/180 = 1/ 9/180= 1 × 180/9 = 20.
6) (4+у)^2-у(у+1)= 16+8у+у^2-у^2-у=16+7у=16+7×(-1/9)=16-7/9= 144-7/9= 137/9 = 15целых 2/9.
7) х^2-ху/12у × 4у/х-у= х(х-у)/12у × 4у/х-у=
= х/12у × 4у= х/3 = 7,8/3 = 2,6.
8) 6/х+5=-5
6/х+5 +5=0
6+5х+25/х+5=0
6+30х/х+5=0
область допустимых значений: х+5 не равно 0
х не равно -5
6+30х=0
30х=-6
х= -6/30
х= -1/5
9) 2х^2+5х-7=0
D= 25 + 7×2×4 = 25+56= 78
х1=-5+√78 / 4
х2=-5-√78 / 4
10) 4(х+10)=-1
4х+40=-1
4х=-1-40
4х=-41
х= -41/4
х= -10,25
11)(5х-2)(-х+3)=-5х^2+15х+2х-6= -5х^2+17х-6
-5х^2+17х-6=0
D=289-6×5×4= 289-120= 169 = 13^2
х1=-17+13 / -5×2 = -4/-10 = 2/5 = 0,4
х2=-17-13 / -5×2 = -30/-10= 3
12) S= 11×13×20 / 4×65/6= 2860 / 2×65/3= 2860/ 130/3 = 2860×3/130 = 22×3 = 66.