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

Toán Lớp 8: giải các phương trình sau bài 4.31 , a, l 2x-5 l=4 b, 3/4-l 2x+1 l=7/8 bài 4.32, a, 6,5 -9/4 : l x + 1/3 l=2 b, 11/4 + 3/2 : l 4x –

Home/ Toán Lớp 8: giải các phương trình sau bài 4.31 , a, l 2x-5 l=4 b, 3/4-l 2x+1 l=7/8 bài 4.32, a, 6,5 -9/4 : l x + 1/3 l=2 b, 11/4 + 3/2 : l 4x –

Toán Lớp 8: giải các phương trình sau bài 4.31 , a, l 2x-5 l=4 b, 3/4-l 2x+1 l=7/8 bài 4.32, a, 6,5 -9/4 : l x + 1/3 l=2 b, 11/4 + 3/2 : l 4x –

Tháng Mười Hai 11, 2022 Toán học 1 Comment 0 views

Toán Lớp 8: giải các phương trình sau
bài 4.31 ,
a, l 2x-5 l=4
b, 3/4-l 2x+1 l=7/8
bài 4.32,
a, 6,5 -9/4 : l x + 1/3 l=2
b, 11/4 + 3/2 : l 4x – 1/5 l =7/2
bài 4.33
a, l 2x-3 l – l 3x+2 l=0
b, l 7x+1 l – l 5x+6 l=0

Comments ( 1 )

  1. tuminh25
    tuminh25
    11 Tháng Mười Hai, 2022 at 4:35 chiều
    Reply
    Giải đáp:
     Bài 4.31
    a)
    |2x-5|=4
    <=>\(\left[ \begin{array}{l}2x-5=4\\2x-5=-4\end{array} \right.\) 
    <=>\(\left[ \begin{array}{l}2x=4+5\\2x=-4+5\end{array} \right.\) 
    <=>\(\left[ \begin{array}{l}2x=4+5\\2x=-4+5\end{array} \right.\)
    <=>\(\left[ \begin{array}{l}2x=9\\2x=1\end{array} \right.\) 
    <=>\(\left[ \begin{array}{l}x=\dfrac{9}{2}\\x=\dfrac{1}{2}\end{array} \right.\) 
    Vậy S={1/2;9/2}
    b)
    3/4 -|2x+1|=7/8
    <=>3/4-7/8=|2x+1|
    <=>6/8-7/8=|2x+1|
    <=>-1/8=|2x+1| (vô lí) [∀x ta có |2x+1|>=0 mà -1/8<0]
    => Phương trình vô nghiệm.
    Vậy S=∅
    Bài 4.32
    a)
    6,5-9/4:|x+1/3|=2
    <=>13/2-9/4:|x+1/3|=2
    <=>13/2 -2=9/4 :|x+1/3|
    <=>9/2=9/4:|x+1/3|
    <=>|x+1/3|=9/4:9/2
    <=>|x+1/3|=9/4 .2/9
    <=>|x+1/3|=1/2
    <=>\(\left[ \begin{array}{l}x+\dfrac{1}{3}=\dfrac{1}{2}\\x+\dfrac{1}{3}=-\dfrac{1}{2}\end{array} \right.\) 
    <=>\(\left[ \begin{array}{l}x=\dfrac{1}{2}-\dfrac{1}{3}\\x=-\dfrac{1}{2}-\dfrac{1}{3}\end{array} \right.\) 
    <=>\(\left[ \begin{array}{l}x=\dfrac{1}{6}\\x=-\dfrac{5}{6}\end{array} \right.\) 
    Vậy S={1/6;-5/6}
    b)
    11/4+3/2:|4x-1/5|=7/2
    <=>3/2 :|4x-1/5|=7/2-11/4
    <=>3/2 : |4x-1/5|=3/4
    <=>|4x-1/5|=3/2:3/4
    <=>|4x-1/5|=3/2 . 4/3
    <=>|4x-1/5|=2
    <=>\(\left[ \begin{array}{l}4x-\dfrac{1}{5}=2\\4x-\dfrac{1}{5}=-2\end{array} \right.\) 
    <=>\(\left[ \begin{array}{l}4x=2+\dfrac{1}{5}\\4x=-2+\dfrac{1}{5}\end{array} \right.\) 
    <=>\(\left[ \begin{array}{l}4x=\dfrac{11}{5}\\4x=-\dfrac{9}{5}\end{array} \right.\) 
    <=>\(\left[ \begin{array}{l}x=\dfrac{11}{20}\\4x=-\dfrac{9}{20}\end{array} \right.\) 
    Vậy S={11/20;-9/20}
    Bài 4.33
    a)
    |2x-3|-|3x+2|=0
    <=>|2x-3|=|3x+2|
    <=>\(\left[ \begin{array}{l}2x-3=3x+2\\2x-3=-(3x+2)\end{array} \right.\) 
    <=>\(\left[ \begin{array}{l}2x-3=3x+2\\2x-3=-3x-2\end{array} \right.\) 
    <=>\(\left[ \begin{array}{l}3x-2x=-3-2\\2x+3x=-2+3\end{array} \right.\) 
    <=>\(\left[ \begin{array}{l}x=-5\\5x=1\end{array} \right.\) 
    <=>\(\left[ \begin{array}{l}x=-5\\x=\dfrac{1}{5}\end{array} \right.\) 
    Vậy S={-5;1/5}
    b)
    |7x+1|-|5x+6|=0
    <=>|7x+1|=|5x+6|
    <=>\(\left[ \begin{array}{l}7x+1=5x+6\\7x+1=-(5x+6)\end{array} \right.\) 
    <=>\(\left[ \begin{array}{l}7x+1=5x+6\\7x+1=-5x-6\end{array} \right.\) 
    <=>\(\left[ \begin{array}{l}7x-5x=6-1\\7x+5x=-6-1\end{array} \right.\) 
    <=>\(\left[ \begin{array}{l}2x=5\\12x=-7\end{array} \right.\) 
    <=>\(\left[ \begin{array}{l}x=\dfrac{5}{2}\\x=-\dfrac{7}{12}\end{array} \right.\) 
    Vậy S={5/2;-7/12}

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

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