Thu gọn biểu thức `a) ( 2x – 3y ) ( 2x + 3y ) – 4 ( x – y ) ² – 8xy` `b) ( 3x – 1 ) ² – 2 ( 3x – 1 ) ( 2x + 3 ) + ( 2x + 3 )

1 bình luận về “Thu gọn biểu thức `a) ( 2x – 3y ) ( 2x + 3y ) – 4 ( x – y ) ² – 8xy` `b) ( 3x – 1 ) ² – 2 ( 3x – 1 ) ( 2x + 3 ) + ( 2x + 3 )”

1. a)(2x-3y)(2x+3y)-4(x-y)^2-8xy

   =(2x)^2-(3y)^2-4.(x^2-2xy+y^2)-8xy

   =4x^2-9y^2-4x^2+8xy-4y^2-8xy

   =(4x^2-4x^2)-(9y^2+4y^2)+(8xy-8xy)

   =-13y^2

   b)(3x-1)^2-2(3x-1)(2x+3)+(2x+3)^2

   =[(3x-1)-(2x+3)]^2

   =(3x-1-2x-3)^2

   =(x-4)^2=x^2-8x+16

   c)(x-2)^3-x(x+1)(x-1)+6x(x-3)

   =x^3-6x^2+12x-8-x(x^2-1)+6x^2-18x

   =x^3+(6x^2-6x^2)+(12x-18x)-8-x^3+x

   =(x^3-x^3)+(x-6x)-8

   =-5x-8

   d)(x-2)(x^2-2x+4)-(x+2)(x^2+2x+4)

   =(x-2)(x^2+2x+4-4x)-(x+2)(x^2-2x+4+4x)

   =(x-2)(x^2+2x+4)-4x(x-2)-(x+2)(x^2-2x+4)-4x(x+2)

   =x^3-8-4x^2+8x-(x^3+8)-4x^2-8x

   =x^3-(4x^2+4x^2)+(8x-8x)-8-x^3-8

   =(x^3-x^3)-8x^2-(8+8)

   =-8x^2-16

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