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

Toán Lớp 8: 2x(x-3)+x(3-2x)=5 b, (x+2)^2 – 3x(x-2)=0

Tháng Sáu 28, 2022 Toán học 2 Comments 0 views

Toán Lớp 8: 2x(x-3)+x(3-2x)=5
b, (x+2)^2 – 3x(x-2)=0

Comments ( 2 )

  1. thanhbinh2k5
    thanhbinh2k5
    28 Tháng Sáu, 2022 at 1:23 chiều
    Reply
    Giải đáp:
     
    Lời giải và giải thích chi tiết:
     2x(x-3)+x(3-2x)=5
    =>2x^2 -6x+3x-2x^2 =5
    =>(2x^2 -2x^2)+(-6x+3x)=5
    =>-3x=5
    =>x= -5/3
    b, (x+2)^2 -3x(x-2)=0
    =>x^2 +4x+4 -3x^2 +6x=0
    =>(x^2 -3x^2 )+(4x+6x)+4=0
    =>-2x^2 +10x+4=0
    =>-2(x^2 -5x -2)=0
    =>x^2 -5x-2=0
    =>(x^2 -5x +25/4) – 33/4=0
    =>(x- 5/2)^2 = 33/4
    $=>(x- \dfrac{5}{2})^{2}=( \sqrt{\dfrac{33}{4}})^{2}$
    =>\(\left[ \begin{array}{l}x -\dfrac{5}{2}= \sqrt{\dfrac{33}{4}}\\ x -\dfrac{5}{2}= -\sqrt{\dfrac{33}{4}}\end{array} \right.\)
    =>\(\left[ \begin{array}{l}x=\dfrac{5 + \sqrt{33}}{2}\\x=\dfrac{5-\sqrt{33}}{2}\end{array} \right.\)
    (Bài tham khảo)

  2. cobelolen
    cobelolen
    28 Tháng Sáu, 2022 at 1:23 chiều
    Reply
    2x(x-3)+x(3-2x) =5
    <=> 2x^2 – 6x+3x-2x^2 =5
    <=> -3x =5
    <=> x = (-5)/3
    Vậy x = -5/3
    $\\$
    (x+2)^2 -3x(x-2) =0
    <=> x^2+4x+4 -3x^2 +6x =0
    <=> -2x^2+10x +4 =0 
    <=> -2(x^2 – 5x -2) =0    
    <=> x^2 -5x -2 =0
    <=> x^2 – 2 . x . 5/2 + 25/4 -33/4 =0
    <=> (x-5/2)^2 =33/4
    <=> \(\left[ \begin{array}{l}x- \dfrac{5}{2} = \sqrt{ \dfrac{33}{4}}\\x- \dfrac{5}{2} = -\sqrt{ \dfrac{33}{4}}\end{array} \right.\) 
    <=> \(\left[ \begin{array}{l}x=\sqrt{ \dfrac{33}{4}} +\dfrac{5}{2} = \dfrac{\sqrt{33}}{2}+ \dfrac{5}{2} \\x= \dfrac{5}{2}-\sqrt{ \dfrac{33}{4}} = \dfrac{5}{2} – \dfrac{\sqrt{33}}{2}\end{array} \right.\) 
    <=> \(\left[ \begin{array}{l}x= \dfrac{\sqrt{33}+5}{2}\\x=\dfrac{5- \sqrt{33}}{2}\end{array} \right.\) 
    $\\$
    Vậy x \in { \frac{\sqrt{33}+5}{2} ; \frac{5- \sqrt{33}}{2}}
     

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

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