Toán Lớp 8: a) (2+xy)² B)(5-3x)² C)(5-x²)(5+x²) D)(5x-1)³ E)(2x-y)(4x²+2xy+y²) F)(x+3)(x²-3x+9)

Question

Toán Lớp 8:  a) (2+xy)² B)(5-3x)² C)(5-x²)(5+x²) D)(5x-1)³ E)(2x-y)(4x²+2xy+y²) F)(x+3)(x²-3x+9)

thaolanphuobg · Answer

Lời giải và giải thích chi tiết:     a)   (2 + xy)^2   = 2^2 + 2 . 2 . xy + (xy)^2   = 4 + 4xy + x^2y^2   b)   (5 - 3x)^2   = 5^2 - 2 . 5 . 3x + (3x)^2   = 25 - 30x + 9x^2   c)   (5 - x^2)(5 + x^2)   = 5^2 - (x^2)^2   = 25 - x^4   d)   (5x - 1)^3   = (5x)^3 - 3 . (5x)^2 + 3 . 5x - 1   = 125x^3 - 75x^2 + 15x - 1   e)   (2x - y)(4x^2 + 2xy + y^2)   = (2x - y)[(2x)^2 + 2x . y + y^2]   = (2x)^3 - y^3   = 8x^3 - y^3   f)   (x + 3)(x^2 - 3x + 9)   = (x + 3)(x^2 - x . 3 + 3^2)   = x^3 - 3^3   = x^3 - 27

maianhtuanh · Answer

#huy   a)(2+xy)^2   =2^2+2.2.xy+(xy)^2   =4+4xy+x^2y^2   b)(5-3x)^2   =5^2-2.5.3x+(3x)^2   =25-30x+9x^2   c)(5-x^2)(5+x^2)   =5^2-(x^2)^2   =25-x^4   d)(5x-1)^3   =(5x)^3-3.(5x)^2+3.5x-1^3   =125x^3-75x^2+15x-1   e)(2x-y)(4x^2+2xy+y^2)   =(2x)^3-y^3   =8x^3-y^3   f)(x+3)(x^2-3x+9)   =(x+3)(x^2-3.x+3^2)   =x^3-3^3   =x^3-27