tìm x a. 2x(x-5)-x(3+2x)=26 b. 49x ² -81=0 03/07/2021 Bởi Charlie tìm x a. 2x(x-5)-x(3+2x)=26 b. 49x ² -81=0
`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
`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
`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}`
`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}.`