Môn Toán Lớp 8: Tìm x: a)(x-2)2-(x1)(x3)-2x=1 ; b)3x(x-7)-2x(x2)=(x1)-3 ; c)(x-1)(x1)-x(x2)=3x-1 ; d)(2x3)2-(x-2)(x2)=3x(x-1)21

Question

Môn Toán Lớp 8:  Tìm x: a)(x-2)^2-(x+1)(x+3)-2x=1  ; b)3x(x-7)-2x(x+2)=(x+1)-3 ; c)(x-1)(x+1)-x(x+2)=3x-1   ; d)(2x+3)^2-(x-2)(x+2)=3x(x-1)+21

lanminhngoc · Answer

Đ&aacute;p     &aacute;n + Lời giải và giải thích chi tiết   :              $  $  $#shinnnnn$  $  $  a)  (x-2)^2 - (x+1)(x+3)-2x=1  => x^2 - 4x+4-x^2 --3x-x-3-2x=1  => -10x+1=1  => -10x=0  => x=0.  Vậy x={0}.  $  $  b)  3x(x-7)-2x(x+2)=(x+1)-3  => 3x(x-7)-2x(x+2)=x+1-3  => 3x(x-7)-2x(x+2)=x-2  => 3x^2 - 21x-2x^2 - 4x=x-2  => x^2 - 25x=x-2  => x^2 - 25x - x + 2=0  => x^2 -26x+2=0  => $ left[ begin{matrix} x= dfrac{26+2  sqrt{167}}{2}  x= dfrac{26-2  sqrt{167}}{2}  end{matrix} right.$   => $ left[ begin{matrix} x=13+  sqrt{167}  x=13-  sqrt{167}  end{matrix} right.$  Vậy x= { 13+ $ sqrt{167}$ hoặc 13- $ sqrt{167}$ } .  $  $  c)  (x-1)(x+1)-x(x+2)=3x-1  => x^2 - 1 - x^2 - 2x=3x-1  => -1-2x=3x-1  => -2x=3x  => 2x+3x=0  => 5x=0  => x=0.  Vậy x={0}.  $  $  d)  (2x+3)^2 - (x-2)(x+2)=3x(x-1)+21  => 4x^2 + 12x+9-x^2 +2^2=3x^2 - 3x+21  => 4x^2 + 12x+9-x^2 +4=3x^2 -3x+21  => 3x^2 + 12x+13=3x^2 -3x+21  =>12x+13=-3x+21  => 12x=-3x+21-13  => 12x=-3x+8  => 12x+3x=8  =>15x=8  => x=8/15.  Vậy x={8/15}.

huenthanh97 · Answer

a)(x-2)^2-(x+1)(x+3)-2x=1           x        2         -    4  x  +    4  -     x        2         -    3  x  -    x  -    3  -    2  x  =    1                -10 x  + 1 = 1               -10 x  = 0                x  = 0               b)3x(x-7)-2x(x+2)=(x+1)-3               3  x  (  x  -    7  )  -    2  x  (  x  +    2  )  =    x  +    1  -    3             3  x  (  x  -    7  )  -    2  x  (  x  +    2  )  =    x  -    2             3   x        2         -    2  1  x  -    2   x        2         -    4  x  =    x  -    2              x        2         -    2  5  x  =    x  -    2              x        2         -    2  5  x  -    x  +    2  =    0              x        2         -    2  6  x  +    2  =    0                 x  =(     26 + 2&radic; 167)/2 ​  ​   ,(     26 - 2&radic; 167)/2                           x  =  1  3  +&radic;    167   ​ ,  1  3  -&radic;    167                        ​​c)(x-1)(x+1)-x(x+2)=3x-1                   x&sup2;   -    1  -     x&sup2;   -    2  x  =    3  x  -    1             -  1  -    2  x  =    3  x  -    1             -  2  x  =    3  x             2  x  +    3  x  =    0             5  x  =    0             x  =    0          d)(2x+3)^2-(x-2)(x+2)=3x(x-1)+21          4   x&and;        2         +    1  2  x  +    9  -     x&and;        2         +    2       2         =    3   x&and;        2         -    3  x  +    2  1               4   x&and;        2         +    1  2  x  +    9  -     x&and;        2         +    4  =    3   x&and;        2         -    3  x  +    2  1               3   x&and;        2         +    1  2  x  +    1  3  =    3   x&and;        2         -    3  x  +    2  1               1  2  x  +    1  3  =    -  3  x  +    2  1               1  2  x  =    -  3  x  +    2  1  -    1  3               1  2  x  =    -  3  x  +    số 8               1  2  x  +    3  x  =    số 8               1  5  x  =    số 8               x  =         số 8/15   ​          ​

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