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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 8: a)(5x-4)2-49×2 b)4×2-9y2+4x-6y c)-x2+5x+2xy-5y-y2 d)x2+4x-12 e)x3+8+6x(x+2) f)(x2+6x+5)(x2+10x+21)+15

Home/ Toán Lớp 8: a)(5x-4)2-49×2 b)4×2-9y2+4x-6y c)-x2+5x+2xy-5y-y2 d)x2+4x-12 e)x3+8+6x(x+2) f)(x2+6x+5)(x2+10x+21)+15

Toán Lớp 8: a)(5x-4)2-49×2 b)4×2-9y2+4x-6y c)-x2+5x+2xy-5y-y2 d)x2+4x-12 e)x3+8+6x(x+2) f)(x2+6x+5)(x2+10x+21)+15

Tháng Một 18, 2023 Toán học 1 Comment 0 views

Toán Lớp 8: a)(5x-4)2-49×2
b)4×2-9y2+4x-6y
c)-x2+5x+2xy-5y-y2
d)x2+4x-12
e)x3+8+6x(x+2)
f)(x2+6x+5)(x2+10x+21)+15

Comments ( 1 )

  1. thucquyenlan
    thucquyenlan
    18 Tháng Một, 2023 at 1:00 chiều
    Reply
    Giải đáp:
    a) -8(x+2)(3x-1)
    b) (2x-3y)(2x+3y+2)
    c) (x-y)(-x+y+5)
    d) (x-2)(x+6)
    e) (x+2)^3
    f) (x+2)(x+4)(x^2+8x+10)
    Lời giải và giải thích chi tiết:
    to Phân tích đa thức thành nhân tử:
    a)
    (5x-4)^2-49x^2
    = (5x-4)^2-(7x)^2
    = (5x-4-7x)(5x-4+7x)
    = (-2x-4)(12x-4)
    = -2(x+2). 4(3x-1)
    = -8(x+2)(3x-1)
    Áp dụng: a^2-b^2 = (a-b)(a+b)
    b)
    4x^2-9y^2+4x-6y
    = (4x^2-9y^2)+(4x-6y)
    = (2x-3y)(2x+3y)+2(2x-3y)
    = (2x-3y)(2x+3y+2)
    Áp dụng: a^2-b^2 = (a-b)(a+b)
    c)
    -x^2+5x+2xy-5y-y^2
    = (-x^2+2xy-y^2)+(5x-5y)
    = -(x^2-2xy+y^2)+5(x-y)
    = -(x-y)^2+5(x-y)
    = (x-y)[-(x-y)+5]
    = (x-y)(-x+y+5)
    Áp dụng: (a-b)^2 = a^2-2ab+b^2
    d)
    x^2+4x-12
    = x^2+6x-2x-12
    = (x^2+6x)-(2x+12)
    = x(x+6)-2(x+6)
    = (x-2)(x+6)
    e)
    x^3+8+6x(x+2)
    = x^3+8+6x^2+12x
    = x^3+6x^2+12x+8
    = x^3+3. x^2. 2+3. x. 2^2+2^3
    = (x+2)^3
    Áp dụng: (a+b)^3 = a^3+3a^2b+3ab^2+b^3
    f)
    (x^2+6x+5)(x^2+10x+21)+15
    = (x^2+5x+x+5)(x^2+7x+3x+21)+15
    = [(x^2+5x)+(x+5)][(x^2+7x)+(3x+21)]+15
    = [x(x+5)+(x+5)][x(x+7)+3(x+7)]+15
    = (x+1)(x+5)(x+3)(x+7)+15
    = [(x+1)(x+7)][(x+5)(x+3)]+15
    = (x^2+7x+x+7)(x^2+3x+5x+15)+15
    = (x^2+8x+7)(x^2+8x+15)+15
    Đặt x^2+8x+7 = a
    = a(a+8)+15
    = a^2+8a+15
    = a^2+5a+3a+15
    = (a^2+5a)+(3a+15)
    = a(a+5)+3(a+5)
    = (a+3)(a+5)
    Thay a= x^2+8x+7 vào ta có:
    = (x^2+8x+7+3)(x^2+8x+7+5)
    = (x^2+8x+10)(x^2+8x+12)
    = (x^2+8x+10)(x^2+4x+2x+12)
    = (x^2+8x+10)[(x^2+4x)+(2x+12)]
    = (x^2+8x+10)[x(x+4)+2(x+4)]
    = (x+2)(x+4)(x^2+8x+10)
     

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222-9+11+12:2*14+14 = ? ( )

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