Giúp mình với ah Bài 1 : tính a,(3-2y)^2 b,(3x+5y)^3 c,(6x-3y)^2 d,(3x+y^5 e,(2x-1)^3 f, 8x^3-y^3

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1. Bài 1:

   $a)(3-2y)^2_{}$

   $⇔4y^2-12y+9_{}$

   $b)(3x+5y)^3_{}$

   $⇔(3x)^3+3.(3x)^2.5y+3.3x(5y)^2+(5y)^3_{}$

   $⇔27x^3+3.9x^2.5y+3.3x.25y^2+125y^3_{}$

   $⇔27x^3+135x^2y+225xy^2+125y^3_{}$

   $+)Nếu_{}$ $(3x+5y)^2_{}$ $thì{}:$

   $⇔(3x)^2+2.3x.5y+(5y)^2_{}$

   $⇔9x^2+30xy+25y^2_{}$

   $c)(6x-3y)^2_{}$

   $⇔(6x)^2-2.6x.3y+(3y)^2_{}$

   $⇔36x^2-36xy+9y^2_{}$

   $d)(3x+y)^2_{}$

   $⇔(3x)^2+2.3xy+y^2_{}$

   $⇔9x^2+6xy+y^2_{}$

   $e)(2x-1)^3_{}$

   $⇔(2x)^3-3.(2x)^2.1+3.2x.1^2-1^3_{}$

   $⇔8x^3-3.4x^2.1+3.2x.1-1_{}$

   $⇔8x^3-12x^2+6x-1_{}$

   $d)8x^3-y^3_{}$

   $⇔2^3x^3-y^3_{}$

   $⇔(2x)^3-y^3_{}$

   $⇔(2x-y).[(2x)^2+2xy+y^2 ] _{}$

   $⇔(2x-y)(4x^2+2xy+y^2)_{}$

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2. Đáp án:

    

   Giải thích các bước giải:

   `a)(3-2y)^2`

   `=3^2-2.3.2y+(2y)^2`

   `=9-12y+4y^2

   `b)(3x+5y)^3`

   `=(3x)^3+3.(3x)^2.5y+3.3x.(5y)^2+(5y)^3`

   `=27x^3+135x^2y+225xy^2+125y^3`

   `c)(6x-3y)^2`

   `=(6x)^2-2.6x.3y+(3y)^2

   `=36x^2-36xy+9y^2`

   `d)(3x+y)^5`

   `=(3x)^5+5.(3x)^4.y+10.(3x)^3.y^2+10.(3x)^2.y^3+5.3x.y^4+y^5`

   `=243x^5+405x^4y+270x^3y^2+90x^2y^3+15xy^4+y^5`

   `e)(2x-1)^3`

   `=(2x)^3-3.(2x)^2.1+3.2x.1^2-1^3`

   `=8x^4-12x^2+6x-1`

   `f)8x^3-y^3`

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

   `=(2x-y)[(2x)^2+2x.y+y^2]`

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

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