\(A=xy\left(x+8y-5\right)-xy\left(7x-5y-1\right)=xy\left[\left(x+8y-5\right)-\left(7x-5y-1\right)\right]=xy\left(-6x+13y-4\right)\)\(Ã=-6x^2y+13xy^2-4xy\)

\(A+B\\ =x^5y^2+7x^2y^4+5xy^3+xy+2+x^2y^4+5xy^3+x^5y^2\\ =\left(x^5y^2+x^5y^2\right)+\left(7x^2y^4+x^2y^4\right)+\left(5xy^3+5xy^3\right)+xy+2\\ =2x^5y^2+8x^2y^4+10xy^3+xy+2\)

`@` `\text {Ans}`

`\downarrow`

`A + B`

`= (x^5y^2 + 7x^2y^4 + 5xy^3 + xy + 2) + (x^2y^4 + 5xy^3 + x^5y^2)`

`= x^5y^2 + 7x^2y^4 + 5xy^3 + xy + 2 + x^2y^4 + 5xy^3 + x^5y^2`

`= (x^5y^2 + x^5y^2) + (7x^2y^4+ x^2y^4) + (5xy^3+ 5xy^3) + xy + 2`

`= 2x^5y^2 + 8x^2y^4 + 10xy^3 + xy + 2`

P(x)+Q(x)

=3x^2y-2x+5xy^2-7y^2+3xy^2-7y^2-9x^2y-x-5

=8xy^2-14y^2-6x^2y-3x-5

=>Chọn A

`@` `\text {Ans}`

`\downarrow`

`A - B`

`= (x^5y^2 + 7x^2y^4 + 5xy^3 + xy + 2) - (x^2y^4 + 5xy^3 + x^5y^2)`

`= x^5y^2 + 7x^2y^4 + 5xy^3 + xy + 2 - x^2y^4 - 5xy^3 - x^5y^2`

`= (x^5y^2 - x^5y^2) + (7x^2y^4 - x^2y^4) + (5xy^3 - 5xy^3) + xy + 2`

`= 6x^2y^4 + xy + 2`

dễ thôi k mik đi rùi mik làm cho

lá sao hả bạn

Lời giải:

$A=x^2-8xy+15y^2=x^2-3xy-(5xy-15y^2)$

$=x(x-3y)-5y(x-3y)=(x-3y)(x-5y)$

$B=2x^2-5xy+2y^2=(2x^2-4xy)-(xy-2y^2)$

$=2x(x-2y)-y(x-2y)=(2x-y)(x-2y)$

$C=2x^2-3y^2-xy=(2x^2+2xy)-(3y^2+3xy)$

$=2x(x+y)-3y(y+x)=(x+y)(2x-3y)$

\(A+7x^2y-5xy^2-xy=x^2y+8xy^2-5xy\)

\(\Rightarrow A=\left(x^2y+8xy^2-5xy\right)-\left(7x^2y-5xy^2-xy\right)\)

        \(=x^2y+8xy^2-5xy-7x^2y+5xy^2+xy\)          \(=\left(x^2y-7x^2y\right)+\left(8xy^2+5xy^2\right)+\left(-5xy+xy\right)\)

 \(=-6x^2y+13xy^2-4xy\)

A = (x\(^2\)y + 8xy\(^2\)- 5xy) - (7x\(^2\)y - 5xy\(^2\)- xy)

A = x\(^2\)y + 8xy\(^2\)- 5xy - 7x\(^2\)y + 5xy\(^2\)+ xy

A = (x\(^2\)y -7x\(^2\)y) + (8xy\(^2\)+ 5xy\(^2\)) + (-5xy +xy)

A = -6x\(^2\)y + 13xy\(^2\)- 4xy

A = (x\(^2\)y + 8xy\(^2\)- 5xy) - (7x\(^2\)y - 5xy\(^2\)-xy)

A = x\(^2\)y + 8xy\(^2\)- 5xy - 7x\(^2\)y + 5xy\(^2\)+xy

A= (x\(^2\)y -7x\(^2\)y) + (8xy\(^2\)+ 5xy\(^2\)) + (-5xy + xy)

A = -6x\(^2\)y + 13xy\(^2\)- 4xy