a) Ta có: \(x^2-7xy+10y^2\)

\(=x^2-2xy-5xy+10y^2\)

\(=x\left(x-2y\right)-5y\left(x-2y\right)\)

\(=\left(x-2y\right)\left(x-5y\right)\)

b) Ta có: \(5x^2+6xy+y^2\)

\(=5x^2+5xy+xy+y^2\)

\(=5x\left(x+y\right)+y\left(x+y\right)\)

\(=\left(x+y\right)\left(5x+y\right)\)

c) Ta có: \(x^2-5x-14\)

\(=x^2-7x+2x-14\)

\(=x\left(x-7\right)+2\left(x-7\right)\)

\(=\left(x-7\right)\left(x+2\right)\)

d) Ta có: \(x^2+2x-15\)

\(=x^2+5x-3x-15\)

\(=x\left(x+5\right)-3\left(x+5\right)\)

\(=\left(x+5\right)\left(x-3\right)\)

2) \(5x^2+6xy+y^2\) 

 \(=9x^2+6xy+y^2-4x^2\)  

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

 \(=\left(3x+y+2x\right)\left(3x+y-2x\right)\) 

 \(=\left(5x+y\right)\left(x+y\right)\) 

3) \(x^2+2xy-15y^2=x^2+2xy+y^2-16y^2\) 

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

  \(=\left(x+y+4y\right)\left(x+y-4y\right)\) 

   \(=\left(x+5y\right)\left(x-3y\right)\) 

hc tốt

a: x^2+4xy-21y^2

\(=x^2+7xy-3xy-21y^2\)

\(=x\left(x+7y\right)-3y\left(x+7y\right)\)

\(=\left(x+7y\right)\left(x-3y\right)\)

b: \(5x^2+6xy+y^2\)

\(=5x^2+5xy+xy+y^2\)

=5x(x+y)+y(x+y)

=(x+y)(5x+y)

c: \(x^2+2xy-15y^2\)

\(=x^2+5xy-3xy-15y^2\)

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

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

d: \(x^2-7xy+10y^2\)

\(=x^2-2xy-5xy+10y^2\)

=x(x-2y)-5y(x-2y)

=(x-2y)(x-5y)

a) \(x^2+4xy-21y^2\)

\(=x^2+7xy-3xy-21y^2\)

\(=x\left(x+7y\right)-3y\left(x+7y\right)\)

\(=\left(x+7y\right)\left(x-3y\right)\)

b) \(5x^2+6xy+y^2\)

\(=5x^2+5xy+xy+y^2\)

\(=5x\left(x+y\right)+y\left(x+y\right)\)

\(=\left(5x+y\right)\left(x+y\right)\)

c) \(x^2+2xy-15y^2\)

\(=x^2+5xy-3xy-15y^2\)

\(=x\left(x+5y\right)-3y\left(x+5y\right)\)

\(=\left(x+5y\right)\left(x-3y\right)\)

d) \(x^2-7xy+10y^2\)

\(=x^2-2xy-5xy+10y^2\)

\(=x\left(x-2y\right)-5y\left(x-2y\right)\)

\(=\left(x-5y\right)\left(x-2y\right)\)

a) x² + 4xy - 21y²

= x² - 3xy + 7xy - 21y²

= (x² - 3xy) + (7xy - 21y²)

= x(x - 3y) + 7y(x - 3y)

= (x - 3y)(x + 7y)

b) 5x² + 6xy + y²

= 5x² + 5xy + xy + y²

= (5x² + 5xy) + (xy + y²)

= 5x(x + y) + y(x + y)

= (x + y)(5x + y)

c) x² + 2xy - 15y²

= x² + 2xy + y² - 16y²

= (x² + 2xy + y²) - 16y²

= (x + y)² - (4y)²

= (x + y - 4y)(x + y + 4y)

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

d) x² - 7xy + 10y²

= x² - 2xy - 5xy + 10y²

= (x² - 2xy) - (5xy + 10y²)

= x(x - 2y) - 5y(x - 2y)

= (x - 2y)(x - 5y)

X²+4xy-21y²=(x²+4xy+4y²)-25y²=(x+2)²-(5y)²=(x+2-5y)(x+2+5y)

5x²+6xy+y²=9x²+6xy+y²-4x²=(3x+y)²-4x²=(3x+y+2x)(3x+y-2x)

(x-y)²+4(x-y)-12=(x-y+2)²-16=(x-y+2+4)(x-y+2-4)

x²-7xy+10y²=x²-7xy+\(\frac{49y^2}{4}-\frac{9y^2}{4}\)= \(\left(x-\frac{7}{2}\right)^2-\left(\frac{3y}{2}\right)^2\)=\(\left(x-\frac{7}{2}-\frac{3y}{2}\right)\left(x-\frac{7}{2}+\frac{3y}{2}\right)\)

x²+2xy-15y²=(x+y)²-16y²=(x+y-4y)(x+y+4y

\(5x^2+10y^2-6xy-4x-2y+3\)

\(=\left(x^2-6xy+9y^2\right)+\left(4x^2-4x+1\right)+\left(y^2-2y+1\right)+1\)

\(=\left(x-3y\right)^2+\left(2x-1\right)^2+\left(y-1\right)^2+1>0\)  (đpcm)

p/s: chúc bạn học tốt

Hi hi mik cảm ơn bn và mik cx chúc bn học tốt nha!!!^-^!!!

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a: \(\left(x-3\right)\left(2x^2-3x+4\right)\)

\(=2x^3-3x^2+4x-6x^2+9x-12\)

\(=2x^3-9x^2+13x-12\)

b: \(\left(4x^2y-5xy^2+6xy\right):2xy\)

\(=\dfrac{4x^2y-5xy^2+6xy}{2xy}\)

\(=\dfrac{2xy\cdot2x-2xy\cdot2,5y+2xy\cdot3}{2xy}\)

\(=2x-2,5y+3\)

c: \(\dfrac{x}{2x+4}-\dfrac{2}{x^3+2x}\)

\(=\dfrac{x\left(x^3+2x\right)-2\left(2x+4\right)}{x\left(x^2+2\right)\cdot2\cdot\left(x+2\right)}\)

\(=\dfrac{x^4+2x^2-4x-8}{2x\left(x^2+2\right)\left(x+2\right)}\)