Register Now

Login

Lost Password

Lost your password? Please enter your email address. You will receive a link and will create a new password via email.

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

Toán Lớp 8: Tìm x biết: 1. 4×2 – 25 – (2x – 5)(x + 7) = 0 2. x3 + 27 + (x + 3)(x – 9) = 0 3. 2×3 + 3×2 + 2x + 3 = 0 4. (x + y + z)3 – x3 – y3 – z

Home/ Toán Lớp 8: Tìm x biết: 1. 4×2 – 25 – (2x – 5)(x + 7) = 0 2. x3 + 27 + (x + 3)(x – 9) = 0 3. 2×3 + 3×2 + 2x + 3 = 0 4. (x + y + z)3 – x3 – y3 – z

Toán Lớp 8: Tìm x biết: 1. 4×2 – 25 – (2x – 5)(x + 7) = 0 2. x3 + 27 + (x + 3)(x – 9) = 0 3. 2×3 + 3×2 + 2x + 3 = 0 4. (x + y + z)3 – x3 – y3 – z

Tháng Bảy 17, 2022 Toán học 1 Comment 0 views

Toán Lớp 8: Tìm x biết:
1. 4×2 – 25 – (2x – 5)(x + 7) = 0
2. x3 + 27 + (x + 3)(x – 9) = 0
3. 2×3 + 3×2 + 2x + 3 = 0
4. (x + y + z)3 – x3 – y3 – z3

Comments ( 1 )

  1. dinhcongson
    dinhcongson
    17 Tháng Bảy, 2022 at 10:06 chiều
    Reply
    1, $4x^{2}$ – 25 – (2x – 5)(x + 7) = 0
    => ($2x)^{2}$ – $5^{2}$ – (2x – 5)(x + 7) = 0
    => (2x – 5)(2x + 5) – (2x – 5)(x + 7) = 0
    => (2x – 5)(2x + 5 – 2x + 7) = 0
    => (2x – 5)(-2) = 0
    => 2x – 5 = 0
    => 2x = 5
    => x = $\frac{5}{2}$ 
    Vậy x = $\frac{5}{2}$
    2, $x^{3}$ + 27 + (x + 3)(x – 9) = 0
    => (x + 3)($x^{2}$ + 3x + 9) + (x + 3)(x – 9) = 0
    => (x + 3)($x^{2}$ + 3x + 9 + x – 9) = 0
    => (x + 3)($x^{2}$ + 4x) = 0
    => x(x + 3)(x + 4) = 0
    => \(\left[ \begin{array}{l}x=0\\x=-3\\x=-4\end{array} \right.\)
    3, $2x^{3}$ + $3x^{2}$ + 2x + 3 = 0
    => ($2x^{3}$ + 2x) + ($3x^{2}$ +3) = 0
    => 2x($x^{2}$ + 1) + 3($x^{2}$ + 1) = 0
    => \(\left[ \begin{array}{l}x=\frac{-3}{2}\\x=-1(loại)\end{array} \right. \)
    Vậy  x = $\frac{-3}{2}$ 
     4, ($x+y+z)^{3}$ – $x^{3}$ – $y^{3}$ – $z^{3}$ 
    = [($x+y+z)^{3}$ – $x^{3}$] – ($y^{3}$ + $z^{3}$) 
    = (x + y + z – x)[($x+y+z)^{2}$ + (x + y + z)x + $x^{2}$] – (y + x)($y^{2}$ + yz + $z^{2}$)  
    = (y + z)($x^{2}$ + $y^{2}$ + $z^{2}$ + 2xy + 2xz + $x^{2}$ + xy + $x^{2}$) – (y + x)($y^{2}$ + yz + $z^{2}$)   
    = (y + z)($3x^{2}$ + $y^{2}$ + $z^{2}$ + 3xy + 3xz + 2yz) – (y + x)($y^{2}$ + yz + $z^{2}$)   
    = (y + z)($3x^{2}$ + $y^{2}$ + $z^{2}$ + 3xy + 3xz + 2yz + $y^{2}$ + yz + $z^{2}$)
    = (y + z)($3x^{2}$ + 3xy + 3xz + 3yz)
    = 3(y + z)($3x^{2}$ + 3xy + 3xz + 3yz)

Leave a reply

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

Việt Hòa

About Việt Hòa