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Bài 6:

M= 2.2 - 2.3+3.2.3

M= 4 - 6 + 18

M= 20

Bài 7: 

P= 1.2 - 5.-1.-2 + 8.-2.2

P = 2 -10 -32

P= -44

Bài 8:

A (thiếu dữ kiện bn ơi)

B= -1.2 . 3.2 + -1.3 +3.3 +-1.3

B= -2 . 6 + -3 + 9 +-3

B= -2 . 6 - 3 + 9 - 3

B= -12 - 3 + 9 - 3

B= -9

a: \(\left(2x+3y\right)\left(x-2y\right)-\dfrac{\left(4x^3y-6x^2y^2-3xy^3\right)}{2xy}\)

\(=2x^2-4xy+3xy-6y^2-\dfrac{2xy\cdot\left(2x^2-3xy-1,5y^2\right)}{2xy}\)
\(=2x^2-xy-6y^2-2x^2+3xy+1,5y^2\)

\(=2xy-4,5y^2\)

b: \(\left(x-2\right)^3-x\left(x+1\right)\left(x-1\right)-\left(3x-1\right)\left(3x-2\right)\)

\(=x^3-6x^2+12x-8-x\left(x^2-1\right)-\left(9x^2-6x-3x+2\right)\)

\(=x^3-6x^2+12x-8-x^3+x-9x^2+9x-2\)

\(=-15x^2+22x-10\)

ta thay \(x=-\dfrac{1}{3};y=\dfrac{1}{2}\)  vào biểu thức ta đc

\(2.\left(-\dfrac{1}{3}\right)^3-5.\left(-\dfrac{1}{3}\right)^2.\left(\dfrac{1}{2}\right)^2-2.\left(-\dfrac{1}{3}\right)^3\cdot\dfrac{1}{2}\)

\(=-\dfrac{2}{9}-5\cdot\dfrac{1}{9}\cdot\dfrac{1}{4}+\dfrac{2}{9}\cdot\dfrac{1}{2}\)

\(=-\dfrac{2}{9}-\dfrac{5}{36}+\dfrac{1}{9}=-\dfrac{1}{4}\)

\(6x^2y^2+x^2y^2-4x^2y^2=\left(6+1-4\right)x^2y^2=3x^2y^2\)

Thay x=3, y=-1 vào biểu thức ta có:
\(3x^2y^2=3.3^2.\left(-1\right)^2=3.9.1=27\)

\(A=3\cdot\dfrac{1}{8}\cdot\dfrac{-1}{3}+6\cdot\dfrac{1}{4}\cdot\dfrac{1}{9}+3\cdot\dfrac{1}{2}\cdot\dfrac{-1}{27}\)

\(=-\dfrac{1}{8}+\dfrac{1}{6}-\dfrac{1}{18}=\dfrac{-9}{72}+\dfrac{12}{72}-\dfrac{4}{72}=-\dfrac{1}{72}\)

Câu b đề sai rồi bạn

a: \(A=3\cdot\dfrac{1}{8}\cdot\dfrac{-1}{3}+6\cdot\dfrac{1}{8}\cdot\dfrac{1}{9}+3\cdot\dfrac{1}{2}\cdot\dfrac{-1}{27}\)

\(=-\dfrac{1}{8}+\dfrac{1}{12}-\dfrac{1}{18}\)

\(=-\dfrac{7}{72}\)

b: \(B=\left(-1\cdot3\right)^2+\left(-1\right)\cdot3+\left(-1\right)^3+3^3\)

\(=9-3-1+27=36-4=32\)

c: \(C=-\dfrac{3}{4}xy^2-2x^2y-\dfrac{9}{2}xy\)

\(=\dfrac{-3}{4}\cdot\dfrac{1}{2}\cdot\left(-1\right)^2-2\cdot\dfrac{1}{4}\cdot\left(-1\right)-\dfrac{9}{2}\cdot\dfrac{1}{2}\cdot\left(-1\right)\)

\(=\dfrac{-3}{8}+\dfrac{1}{2}+\dfrac{9}{4}=\dfrac{19}{8}\)

1.

\(a,\left(-xy\right)\left(-2x^2y+3xy-7x\right)\)

\(=2x^3y^2-3x^2y^2+7x^2y\)

\(b,\left(\dfrac{1}{6}x^2y^2\right)\left(-0,3x^2y-0,4xy+1\right)\)

\(=-\dfrac{1}{20}x^4y^3-\dfrac{1}{15}x^3y^3+\dfrac{1}{6}x^2y^2\)

\(c,\left(x+y\right)\left(x^2+2xy+y^2\right)\)

\(=\left(x+y\right)^3\)

\(=x^3+3x^2y+3xy^2+y^3\)

\(d,\left(x-y\right)\left(x^2-2xy+y^2\right)\)

\(=\left(x-y\right)^3\)

\(=x^3-3x^2y+3xy^2-y^3\)

2.

\(a,\left(x-y\right)\left(x^2+xy+y^2\right)\)

\(=x^3-y^3\)

\(b,\left(x+y\right)\left(x^2-xy+y^2\right)\)

\(=x^3+y^3\)

\(c,\left(4x-1\right)\left(6y+1\right)-3x\left(8y+\dfrac{4}{3}\right)\)

\(=24xy+4x-6y-1-24xy-4x\)

\(=\left(24xy-24xy\right)+\left(4x-4x\right)-6y-1\)

\(=-6y-1\)

#Toru