Tìm x a, (3x-1)(2x+7)-(x+1)(6x-5) = 16 b,(10x+9)x-(5x-1)(2x+3)=8 c, (3x-5)(7-5x)+(5x+2)(3x-2)-2 = 0

0 bình luận về “Tìm x a, (3x-1)(2x+7)-(x+1)(6x-5) = 16 b,(10x+9)x-(5x-1)(2x+3)=8 c, (3x-5)(7-5x)+(5x+2)(3x-2)-2 = 0”

1. ` a) (3x-1)(2x+7)-(x+1)(6x-5) = 16`

   `⇔(6x^2+19x−7)-(6x^2+x−5)=16`

   `⇔6x^2+19x−7-6x^2-x+5=16`

   `⇔(6x^2-6x^2)+(19x−x)+(5-7)=16`

   `⇔18x-2=16`

   `⇔18x-2-16`

   `⇔18x-18=0`

   `⇔18(x-1)=0`

   `⇔x-1=0`

   `⇔x=0+1`

   `⇔x=1.`

   Vậy `x=1.`

   `b)(10x+9)x-(5x-1)(2x+3)=8`

   `⇔(10x^2+9x)-(10x^2+13x−3)=8`

   `⇔10x^2+9x-10x^2-13x+3=8`

   `⇔(10x^2-10x^2)+(9x-13x)+3-8=0`

   `⇔-4x-5=0`

   `⇔-4x=0+5`

   `⇔-4x=5`

   `⇔x=5:(-4)`

   `⇔x=-5/4.`

   Vậy `x=-5/4.`

   `c)(3x-5)(7-5x)+(5x+2)(3x-2)-2 = 0`

   `⇔(−15×2+46x−35)+(15x^2−4x−4)=0`

   `⇔−15×2+46x−35+15x^2−4x−4-2=0`

   `⇔(-15x^2+15x^2)+(46x-4x)-(35+4+2)=0`

   `⇔42x-41=0`

   `⇔42x=0+41`

   `⇔42x=41`

   `⇔x=41:42`

   `⇔x=41/42.`

   Vậy `x=41/42.`

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2. Đáp án:

    a) `(3x-1)(2x+7)-(x+1)(6x-5)=16`

   `<=>6x^2+21x-2x-7-6x^2+5x-6x+5-16=0`

   `<=>18x=-18`

   `<=>x=-1`

   Vậy `x = -1`

   b) `(10x+9)x-(5x-1)(2x+3)=8`

   `<=>10x^2+9x-10x^2-15x+2x+3-8=0`

   `<=>-4x=5`

   `<=>x=-5/4`

   Vậy `x=-5/4`

   c) `(3x-5)(7-5x)+(5x+2)(3x-2)-2=0`

   `<=>21x-15x^2-35+25x+15x^2-10x+6x-4-2=0`

   `<=>42x=-41`

   `<=>x=-41/42`

   Vậy `x=-41/42`

   Giải thích các bước giải:

    

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