Trả lời:

\(9x^2+2y^2-6xy-4y+4\)

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

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

`a,(x+y)^2`

`b, x^2-25`

`=x^2-5^2`

`=(x-5)(x+5)`

a) (x+y)^{2}=x^2+2xy+y^2

b) x^2 -25=x^2 - 5^2=(x-5)(x+5)

a) (x + y)² = x² + 2xy + y²

b) x² - 25 = x² - 5² = (x - 5)(x + 5)

\(\left(2a-b\right)^2-4\left(a-b\right)^2\)

\(=\left(2a\right)^2-2.2a.b+b^2-4.a^2-2.a.b+b^2\)

\(=4a^2-4ab+b^2-4a^2-2ab+b^2\)

\(=-6ab+2b^2\)

\(\left(2a-b\right)^2-4\left(a-b\right)^2=4a^{^2}-4ab+b^2-4\left(a^2-2ab+b^2\right)=4a^2-4ab+b^2-4a^2+8ab-4b^2=4ab-3b^2=b\left(4a-3b\right)\)

`9x^2+4y^2-12xy+6x-4y+1`

`=(3x)^2-2.3x.2y+(2y)^2+2(3x-2y)+1`

`=(3x-2y)^2+2(3x-2y)+1`

`=(3x-2y+1)^2`

9x²+4y²-12xy+6x-4y+1=(3x-2y+1)²

\(=\left(\dfrac{3}{4}-\dfrac{1}{2}x\right)\left(\dfrac{3}{4}+\dfrac{1}{2}x\right)\)

\(\dfrac{9}{16}-\dfrac{1}{4}x^2=\left(\dfrac{3}{4}-\dfrac{1}{2}x\right)\left(\dfrac{3}{4}+\dfrac{1}{2}x\right)\)

\(25a^2+4b^2-20ab\)

\(=\left(5a\right)^2-2\cdot5a\cdot2b+\left(2b\right)^2\)

\(=\left(5a-2b\right)^2\)

\(=\left(5a\right)^2-2.5.2ab+\left(2b\right)^2=\left(5a-2b\right)^2\)

cái trên của bạn có sai không vậy ?? hình như chỗ -2x phải là -12x

8-12x+6x-x³ =(2-x)³

8-12x+6x²-x³=2³-3.2²x+3.2.x²-x³=(2-x)³

^ok?

giải : 8-2x+6x² -x³ =(2-x)³

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