Bài 5 : Hằng đẳng thức dạng ( A – B )^3 = A^3 -3A^2B + 3AB^2 – B^3 a) – ( 4 – 2y )^3 b) – ( a – 2 )^3 c) ( 2x – 3y )^3 d) ( x -1/3 y)^3

0 bình luận về “Bài 5 : Hằng đẳng thức dạng ( A – B )^3 = A^3 -3A^2B + 3AB^2 – B^3 a) – ( 4 – 2y )^3 b) – ( a – 2 )^3 c) ( 2x – 3y )^3 d) ( x -1/3 y)^3”

1. a) – (4 – 2y)^3

   = – [4^3 – 3.4^2.2y + 3.4.(2y)^2 – (2y)^3]

   = – (64 – 96y + 48y^2 – 8y^3)

   = -64 + 96y – 48y^2 + 8y^3

   b) – (a – 2)^3

   = – (a^3 – 3.a^2.2 + 3.a.2^2 – 2^3)

   = – (a^3 – 6a^2 + 12a – 8)

   = -a^3 + 6a^2 – 12a + 8

   c) (2x – 3y)^3

   = (2x)^3 – 3.(2x)^2.3y + 3.2x.(3y)^2 – (3y)^3

   = 8x^3 – 36x^2y + 54xy^2 – 27y^3

   d) (x -1/3y)^3

   = x^3 – 3.x^2.1/3y + 3.x.(1/3y)^2 – (1/3y)^3

   = x^3 – x^2y + 1/3xy^2 – 1/27y^3

   #Peach Tea

   Bình luận

2. \[a) – (4 – 2y)^3 = – [4^3 – 3.4^2.2y + 3.4.(2y)^2 – (2y)^3] = – (64 – 96y + 48y^2 – 8y^3) = -64 + 96y – 48y^2 + 8y^3\]

   \[b) – (a – 2)^3 = – (a^3 – 3.a^2.2 + 3.a.2^2 – 2^3) = – (a^3 – 6a^2 + 12a – 8) = -a^3 + 6a^2 – 12a + 8\]

   \[c) (2x – 3y)^3 = (2x)^3 – 3.(2x)^2.3y + 3.2x.(3y)^2 – (3y)^3 = 8x^3 – 36x^2y + 54xy^2 – 27y^3\]

   \[d) (x -1/3y)^3 = x^3 – 3.x^2.1/3y + 3.x.(1/3y)^2 – (1/3y)^3 = x^3 – x^2y + 1/3xy^2 – 1/27y^3\]

   Bình luận