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

Toán Lớp 8: a) (3x + 4)2 – (3x – 1)(3x + 1) = 49 b) x2 – 4x + 4 = 9(x – 2) c) x2 – 25 = 3x – 15 d) (x – 1)3 + 3(x + 1)2 = (x2 – 2x + 4)(x + 2) Gi

Home/ Toán Lớp 8: a) (3x + 4)2 – (3x – 1)(3x + 1) = 49 b) x2 – 4x + 4 = 9(x – 2) c) x2 – 25 = 3x – 15 d) (x – 1)3 + 3(x + 1)2 = (x2 – 2x + 4)(x + 2) Gi

Toán Lớp 8: a) (3x + 4)2 – (3x – 1)(3x + 1) = 49 b) x2 – 4x + 4 = 9(x – 2) c) x2 – 25 = 3x – 15 d) (x – 1)3 + 3(x + 1)2 = (x2 – 2x + 4)(x + 2) Gi

Tháng Bảy 21, 2022 Toán học 2 Comments 0 views

Toán Lớp 8: a) (3x + 4)2 – (3x – 1)(3x + 1) = 49 b) x2 – 4x + 4 = 9(x – 2)
c) x2 – 25 = 3x – 15 d) (x – 1)3 + 3(x + 1)2 = (x2 – 2x + 4)(x + 2)
Giúp mình với ạ

Comments ( 2 )

  1. thudan
    thudan
    21 Tháng Bảy, 2022 at 5:40 sáng
    Reply
    Giải đáp + Lời giải và giải thích chi tiết !
    to Tìm x:
    a)
    (3x+4)^2-(3x-1)(3x+1) = 49
    <=> 9x^2+24x+16-9x^2+1 = 49
    <=> (9x^2-9x^2)+24x+(16+1) = 49
    <=> 24x+17 = 49
    <=> 24x = 32
    <=> x = 4/3
    Vậy S= {4/3}
    b)
    x^2-4x+4 = 9(x-2)
    <=> (x^2-4x+4)-9(x-2) = 0
    <=> (x-2)^2-9(x-2) = 0
    <=> (x-2)(x-2-9) = 0
    <=> (x-2)(x-11) = 0
    <=> \(\left[ \begin{array}{l}x-2=0\\x-11=0\end{array} \right.\) 
    <=> \(\left[ \begin{array}{l}x=2\\x=11\end{array} \right.\) 
    Vậy S= {2; 11}
    c)
    x^2-25 = 3x-15
    <=> (x^2-25)-3x+15 = 0
    <=> (x^2-25)-(3x-15) = 0
    <=> (x-5)(x+5)-3(x-5) = 0
    <=> (x-5)(x+5-3) = 0
    <=> (x-5)(x+2) = 0
    <=> \(\left[ \begin{array}{l}x-5=0\\x+2=0\end{array} \right.\) 
    <=> \(\left[ \begin{array}{l}x=5\\x=-2\end{array} \right.\) 
    Vậy S= {5; -2}
    d)
    (x-1)^3+3(x+1)^2 = (x^2-2x+4)(x+2)
    <=> (x^3-3x^2+3x-1)+3(x^2+2x+1) = x^3+2^3
    <=> x^3-3x^2+3x-1+3x^2+6x+3-x^3-8 = 0
    <=> (x^3-x^3)+(-3x^2+3x^2)+(3x+6x)+(-1+3-8) = 0
    <=> 9x-6 = 0
    <=> 9x = 6
    <=> x = 2/3
    Vậy S= {2/3}
     

  2. kimnguenoanh
    kimnguenoanh
    21 Tháng Bảy, 2022 at 5:40 sáng
    Reply
    a)
    (3x+4)^2 – (3x-1)(3x+1) = 49
    => [(3x)^2+2.3x.4+4^2] -[(3x)^2-1^2]=49
    => (9x^2+24x+16)-(9x^2-1)=49
    => 9x^2+24x+16-9x^2+1=49
    =>(9x^2-9x^2)+24x=49-16-1
    => 24x = 32
    =>x=4/3
    Vậy x=4/3
    b)
    x^2-4x+4=9(x-2)
    <=> x^2-  2.x.2+2^2 = 9 (x-2)
    <=> (x-2)^2 = 9 (x-2)
    <=> (x-2)^2 – 9 (x-2) =0
    <=> (x-2) (x-2-9)=0
    <=>(x-2)(x-11)=0
    <=>x-2=0 hoặc x-11=0
    +)x-2=0=>x=2
    +)x-11=0=>x=11
    Vậy x\in{2;11}
    c)
    x^2 – 25 = 3x-15
    => x^2 – 25 – 3x + 15 =0
    => x^2 – 3x -10=0
    => x^2 – 5x + 2x – 10=0
    => x(x-5) + 2 (x-5)=0
    =>(x-5)(x+2)=0
    =>x-5=0 hoặc x+2=0
    +)x-5=0=>x=5
    +)x+2=0=>x=-2
    Vậy x\in{5;-2}
    d)
    (x-1)^3 + 3 (x+1)^2 = (x^2 – 2x+4)(x+2)
    => (x^3 – 3 . x^2 . 1 + 3 . x . 1^2 – 1^3) + 3 (x^2 + 2x+1) = (x^2-  x . 2 + 2^2)(x+2)
    => (x^3 – 3x^2 + 3x – 1) + (3x^2+6x+3) = x^3 + 2^3
    => x^3  – 3x^2 + 3x  – 1 + 3x^2 + 6x + 3 = x^3 + 8
    => x^3  – 3x^2 + 3x  – 1 + 3x^2 + 6x + 3 – x^3 – 8=0
    => (x^3 – x^3) + (3x^2-  3x^2) + (6x+3x) + (3-1-8)=0
    => 9x -6=0
    =>9x=6
    =>x=2/3
    Vậy x=2/3

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

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