\(\frac{1}{x}+\frac{1}{y}+\frac{1}{z}=\frac{1}{x+y+z}\)

\(\Rightarrow\frac{1}{x}+\frac{1}{y}+\frac{1}{z}-\frac{1}{x+y+z}=0\)

\(\Leftrightarrow\frac{yz\left(x+y+z\right)+xz\left(x+y+z\right)+xy\left(x+y+z\right)-xyz}{xyz\left(x+y+z\right)}=0\)

\(\Leftrightarrow\)\(xyz+y^2z+yz^2+x^2z+xyz+xz^2+x^2y+xy^2+xyz-xyz=0\)

\(\Leftrightarrow\)\(\left(xyz+y^2z\right)+\left(xyz+x^2z\right)+\left(xz^2+yz^2\right)+\left(xy^2+x^2y\right)=0\)

\(\Leftrightarrow yz\left(x+y\right)+xz\left(x+y\right)+z^2\left(x+y\right)+xy\left(x+y\right)=0\)

\(\Leftrightarrow\left(x+y\right)\left(yz+xz+xy+z^2\right)=0\)

\(\Leftrightarrow\left(x+y\right)\left(x+z\right)\left(y+z\right)=0\)

\(\Rightarrow\orbr{\begin{cases}x+y\\x+z=0\end{cases}}=0\)  hoặc y+z=0

Do đó ta có B=0

Số thứ 3= trung bình cộng của số thứ 1 và số thứ 2 nên số thứ thứ 3= trung bình cộng của 3 số là 5/8

Tổng của số thứ 1 và số thứ 2 là:5/8x2=10/8

Số thứ 2 là:[5/4-1/4]:2=1/2

Số thứ 1 là:1/2+1/4=3/4

Số thứ ba là:5/8

- Sang chơi nhà Dế Choắt thì hết sức chê bai nhà cửa: luộm thuộm, bề bộn, tuềnh toàng,... Dế Choắt xin đào giúp một ngách sang nhà Dế Mèn thì chú ta khinh khỉnh, ích kỉ không cho và nói những lời phỉ báng.

→ Thái độ của Dế Mèn đối với Dế Choắt rất khó chịu, vừa thể hiện sự trịch thượng kẻ cả, vừa thể hiện sự ích kỉ, khinh thường.

\(\left(100-88+99\right):3\)

\(=\left(12+99\right):3\)

\(=111:3\)

\(=37\)

Vậy đây là phép chia hết nên số dư bằng 0

chuc bn hoc tốt!

17 000 . 9 + 17 000

= 17 000 . 9 + 17 000 . 1

=   17 000 . ( 9 + 1 )

= 17 000 . 10

= 170 000

\(\frac{1}{20}=0,05.\)em nhe.

\(\frac{1}{20}=2,1\left(SAI\right)\)

17000.9 + 17000= 170 000

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hàng đơn vị: a+b+c=c =>a+b=10(vì ko có 2 số 1 chữ số nào có tổng la 20)

hàng chục: a+b+c=a =>b+c=9(vì nhớ 1 ở hàng đơn vị)

hàng trăm: =>b=1(vì nhớ 1 ở hàng chục)

=>a=10-b=10-1=9

c=9-b=9-1=8