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1A,B,D
2 M=2
3 \(=\dfrac{3}{4x}\)
4 \(=\dfrac{4\left(x+y\right)}{x-y}=\dfrac{4x+4y}{x-y}\)
5 K rút gọn đc
6 \(=\dfrac{4\left(x-1\right)+2\left(x-1\right)}{6\left(x-1\right)}=\dfrac{6\left(x-1\right)}{6\left(x-1\right)}=1\)
a, \(\left(5x-4\right)\left(5x+4\right)-\left(5x-4\right)^2=\left(25x^2-16\right)-\left(25x^2-40x+16\right)=40x-32\)
b,\(\left(5x+3\right)^2-\left(4x-1\right)^2-\left(9x^2+8\right)=\left(x+4\right)\left(9x-2\right)-\left(9x^2+8\right)\)
\(=9x^2+34x-8-\left(9x^2+8\right)=34x\)
c,\(2\left(x-5y\right)\left(x+5y\right)+\left(x+5y\right)^2+\left(x-5y\right)^2=\left(2x\right)^2=4x^2\)
\(\left(x^2+\frac{2}{5}y\right)\left(x^2-\frac{2}{5}y\right)\)
\(=x^4+\frac{2}{5}x^2y-\frac{2}{5}x^2y-\left(\frac{2}{5}y\right)^2\)
\(=x^4-\frac{4}{25}y^2\)
`@` `\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`
`= 6x^2y^4 + xy + 2`
\(A+B\\ =x^5y^2+7x^2y^4+5xy^3+xy+2+x^2y^4+5xy^3+x^5y^2\\ =\left(x^5y^2+x^5y^2\right)+\left(7x^2y^4+x^2y^4\right)+\left(5xy^3+5xy^3\right)+xy+2\\ =2x^5y^2+8x^2y^4+10xy^3+xy+2\)
`@` `\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`
\(A=\left(\dfrac{1}{5}-\dfrac{2}{3}+1\right)x^5y=\dfrac{8}{15}x^5y\)
Thay x = -1 ; y = 2 ta được \(A=\dfrac{-16}{15}\)
\(A=5x^2-3x-x^3+x^2+x^3-62x-10+3x\\ A=6x^2-62x-10\\ B=x^3+x^2+x-x^3-x^2-x+5=5\\ C=3x^2y-15xy^2+15xy^2-10y^3+10y^2-3x^2y-4=-4\)
b: Ta có: \(B=x\left(x^2+x+1\right)-x^2\left(x+1\right)-x+5\)
\(=x^3+x^2+x-x^3-x^2-x+5\)
=5