(a+b)^3+(a-b)^3-2a^3 (x+y)^2-(x-y)^2 9^8.2^8-(18^4-1).(18^4+1)

2 bình luận về “(a+b)^3+(a-b)^3-2a^3 (x+y)^2-(x-y)^2 9^8.2^8-(18^4-1).(18^4+1)”

1. 1.

   (a+b)^3+(a-b)^3-2a^3

   =a^3+3a^2b+3ab^2+b^3+a^3-3a^2b+3ab^2-b^3-2a^3

   =(a^3+a^3-2a^3)+(3a^2b-3a^2b)+(3ab^2+3ab^2)+(b^3-b^3)

   =6ab^2

   2.

   (x+y)^2-(x-y)^2

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

   =2y.2x

   =4xy

   3.

   9^8 .2^8-(18^4-1).(18^4+1)

   =(9.2)^8-[(18^4)^2-1^2]

   =18^8-(18^8-1)

   =18^8-18^8+1

   =1

   Trả lời
2. (a+b)^3 + (a-b)^3 – 2a^3

   = a^3 + 3a^2b + 3ab^2 + b^3 + a^3 – 3a^2b + 3ab^2 – b^3 – 2a^3

   = (a^3 + a^3 – 2a^3) + (3a^2b – 3a^2b) + (3ab^2 + 3ab^2) + (b^3 – b^3)

   = 0 + 0 + 6ab^2 + 0

   = 6ab^2

   (x+y)^2 – (x-y)^2

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

   = 2y . 2x

   = 4xy

   9^8  . 2^8 – (18^4-1)(18^4+1)

   = (9 . 2)^8 – [(18^4)^2 – 1^2]

   = 18^8 – (18^8 – 1)

   = 18^8 – 18^8 +1

   = 1

   Trả lời