Tìm x biết: a) $\frac{2}{3}x-\frac{1}{7}=\frac{1}{4}$ b) $x+\frac{2}{5}=\frac{5}{7}$ c) $(2x+3)^{2}+11=36$
2 câu trả lời
Đáp án:
`a) 33/56`
`b) 11/35 `
`c) {1 ; -4 }`
Giải thích các bước giải:
`a)
`2/3 x - 1/7 = 1/4 `
`2/3 x = 1/4 + 1/7`
`2/3 x = 11/28 `
`x = 11/28 : 2/3 `
`x = 33/56 `
`b)`
`x + 2/5 = 5/7 `
`x = 5/7 - 2/5 `
`x = 11/35 `
`c)`
`( 2x + 3 )^2 + 11 = 36 `
`(2x + 3 )^2 = 25 `
`25 = 5^2 `
`=>`
`2x + 3 = 5 `
`2x = 5 - 3 `
`x = 2 : 2 `
`x = 1 `
`TH_2`
`(2x + 3 )^2 = (-5)^2 `
`2x + 3 = -5 `
`2x = -8`
`x = -4`
Lời giải:
`a, 2/3x - 1/7 = 1/4`
`2/3x = 1/4 + 1/7`
`2/3x = 7/28 + 4/28`
`2/3x = 11/28`
`x = 11/28 : 2/3`
`x = 11/28 * 3/2`
`x = 33/56`
Vậy `x = 33/56`
`b, x + 2/5 = 5/7`
`x = 5/7 - 2/5`
`x = 25/35 - 14/35`
`x = 11/35`
Vậy `x = 11/35`
`c, (2x + 3)^2 + 11 = 36`
`(2x + 3)^2 = 36 - 11`
`(2x + 3)^2 = 25`
`(2x + 3)^2 = 5^2` hoặc `(2x + 3) = (-5)^2`
$\left[\begin{matrix} 2x + 3 = 5\\ 2x + 3 = -5\end{matrix}\right.$
$\left[\begin{matrix} 2x = 2\\ 2x = -8\end{matrix}\right.$
$\left[\begin{matrix} x = 1\\ x = -4\end{matrix}\right.$
Vậy `x = 1` hoặc `x = -4`
