Tìm x
a, ( x + 3/4 ) ² = 4/25
b, ( 4/7 – 1/2 x ) ³ = 8
C, x³ = -8
D, 9^x-1 = 1/9
Tìm x a, ( x + 3/4 ) ² = 4/25 b, ( 4/7 – 1/2 x ) ³ = 8 C, x³ = -8 D, 9^x-1 = 1/9
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Mít Mít
$a, ( x + \dfrac{3}{4} ) ² = \dfrac{4}{25}$
$ ( x+ \dfrac{3}{4})²$ = $\frac{2²}{5²}$
$ x + \dfrac{3}{4}$ = $±\dfrac{2}{5}$
TH1:
$ x + \dfrac{3}{4}$ = $\dfrac{2}{5}$
$x = \dfrac{2}{5}$ – $\dfrac{3}{4}$
$x =\dfrac{-7}{20} $
TH2:
$ x + \dfrac{3}{4} = -\dfrac{2}{5}$
$x =-\dfrac{2}{5} -\dfrac{3}{4}$
$x =\dfrac{-23}{20} $
$b, ( \dfrac{4}{7} – \dfrac{1}{2}x ) ³ = 8$
$( \dfrac{4}{7} -\dfrac{1}{2}x ) ³ = 2³$
$\dfrac{4}{7} -\dfrac{1}{2}x = 2$
$ -\dfrac{1}{2}x $= 2- $\dfrac{4}{7} $
$ -\dfrac{1}{2}x$ = $\dfrac{10}{7} $
$x = \dfrac{10}{7} $ : $\dfrac{-1}{2} $
$x = \dfrac{20}{7}$
$c, x³ = -8$
$x³ = -2³$
$x = -2$
$D, 9^{x-1} =\dfrac{1}{9} $
$9^{x-1} =9^{-1}$
$x – 1 = -1 $
$x = -1 +1 $
$x = 0 $
#no copy #
Latifah
`a` , ( `x` `+` `3/4` ) ² `=` `4/25`
⇒ ( `x` `+` `3/4` ) ² `=` (`±2/5`) ²
⇒ `x` `+` `3/4` `=` `±2/5`
Trường hợp 1:
⇒ `x` `+` `3/4` `=` `2/5`
⇒ `x` `=` `2/5` `-` `3/4`
⇒ `x` `=` `-7/20`
Trường hợp 2:
`x` `+` `3/4` `=` `-2/5`
⇒ `x` `=` `-2/5` `-` `3/4`
⇒ `x` `=` `-23/20`
`b` , ( `4/7` `-` `1/2` `x` ) ³ `=` `8`
⇒ ( `4/7` `-` `1/2` `x` ) ³ `=` $2^{3}$
⇒ `4/7` `-` `1/2` `x` `=` `2`
⇒ `1/2` `x` `=` `4/7` `-` `2`
⇒ `1/2` `x` `=` `-10/7`
⇒ `x` `=` `-10/7` `:` `1/2`
⇒ `x` `=` `-20/7`
`c` , $x^{3}$ `=` `-8`
⇒ $x^{3}$ `=` $-2^{3}$
⇒ `x` `=` `-2`
`d` , $9^{x-1}$ `=` `1/9`
⇒ $9^{x-1}$ `=` $9^{-1}$
⇒ `x` `-` `1` `=` `-1`
⇒ `x` `=` `-1` `+` `1`
⇒ `x` `=` `0`