Toán Lớp 8: 1.(2x-y)^2 2.(x+4y)^2 3.4x^2-9y^2 4.27x^3-8 5.(x+2y)^3 6.(3x-7)^3 7.8x^3+27 7 hang dang thuc

Question

Toán Lớp 8:  1.(2x-y)^2 2.(x+4y)^2 3.4x^2-9y^2 4.27x^3-8 5.(x+2y)^3 6.(3x-7)^3 7.8x^3+27 7 hang dang thuc

maianhnhiquynh · Answer

#Sad   1)   (2x-y)^2   = (2x)^2-2. 2x. y+y^2   = 4x^2-4xy+y^2   2)   (x+4y)^2   = x^2+2. x. 4y+(4y)^2   = x^2+8xy+16y^2   3)   4x^2-9y^2   = (2x)^2-(3y)^2   = (2x-3y)(2x+3y)   4)   27x^3-8   = (3x)^3-2^3   = (3x-2)[(3x)^2+3x. 2+2^2]   = (3x-2)(9x^2+6x+4)   5)   (x+2y)^3   = x^3+3. x^2. 2y+3. x. (2y)^2+(2y)^3   = x^3+6x^2y+12xy^2+8y^3   6)   (3x-7)^3   = (3x)^3-3. (3x)^2. 7+3. 3x. 7^2-7^3   = 27x^3-189x^2+441x-343   7)   8x^3+27   = (2x)^3+3^3   = (2x+3)[(2x)^2-2x. 3+3^2]   = (2x+3)(4x^2-6x+9)

thudan · Answer

1.(2x-y)^2 = (2x)^2 - 2.2x.y + y^2 = 4x^2 - 4xy + y^2$  $  2.(x+4y)^2 = x^2 + 2.x.4y + (4y)^2 = x^2 + 8xy +16y^2$  $  3.4x^2-9y^2 = (2x)^2 - (3y)^2 = (2x-3y)(2x+3y) $  $  4.27x^3-8 = (3x)^3 - 2^3 = (3x-2)(9x^2 + 6x + 4)  $  $  5.(x+2y)^3 = x^3 + 3.x^2.2y + 3.x.(2y)^2 + (2y)^3 = x^3 + 6x^2y + 12xy^2 + 8y^3$  $  6.(3x-7)^3 = (3x)^3 - 3.(3x)^2.7 + 3.3x.7^2 - 7^3 = 27x^3 - 189x^2 + 441x - 343 $  $  7. 8x^3+27 = (2x+3)(4x^2 - 6x + 9)    Ch&uacute;c bạn học tốt.