tìm x a. 2x(x-5)-x(3+2x)=26 b. 49x ² -81=0

tìm x
a. 2x(x-5)-x(3+2x)=26
b. 49x ² -81=0

0 bình luận về “tìm x a. 2x(x-5)-x(3+2x)=26 b. 49x ² -81=0”

  1. `a. 2x(x-5)-x(3+2x)=26`

    `<=>2x^2-10x-3x-2x^2=26`

    `<=>2x^2-2x^2-10x-3x=26`

    `<=>-13x=26`

    `<=>x=-2`

    Vậy `S={-2}`

    `b. 49x ² -81=0`

    `<=>49x^2-9^2=0`

    `<=>(7x-9)(7x+9)=0`

    `<=>`\(\left[ \begin{array}{l}7x-9=0\\7x+9=0\end{array} \right.\)

    `<=>`\(\left[ \begin{array}{l}x=9/7\\x=-9/7\end{array} \right.\)

    Vậy `S={9/7;-9/7}`

    Bình luận
  2. `a)2x(x-5)-x(3+2x)=26`

    `⇔2x.x+2x.(-5)+(-x).3+(-x).2x=26`

    `⇔2x^2-10x-3x-2x^2=26`

    `⇔-13x=26`

    `⇔x=26:(-13)

    `⇔x=-2`

    Vậy `S=-2`

    `b)49x^2-81=0`

    `⇔(7x)^2-9^2=0`

    `⇔(7x-9)(7x+9)=0`

    `⇔`\(\left[ \begin{array}{l}7x-9=0\\7x+9=0\end{array} \right.\) 

    `⇔`\(\left[ \begin{array}{l}7x=9\\7x=-9\end{array} \right.\) 

    `⇔`\(\left[ \begin{array}{l}x=\dfrac{9}{7}\\x=\dfrac{-9}{7}\end{array} \right.\) 

    Vậy `S={9/7;-9/7}.`

    Bình luận

Viết một bình luận