Tìm x , biết : a, (1/2) mũ 2 . x-1= 1/8 b, (2x + 1) mũ 3 = -8 c, ( 2x - 1) mũ 2 bằng 9/16

Đáp án:

 

Giải thích các bước giải:

`a)(1/2)^2.x-1=1/8.`

`⇒1/4.x-1=1/8.`

`⇒1/4.x=1/8+1.`

`⇒1/4.x=1/8+8/8.`

`⇒1/4.x=9/8.`

`⇒x=9/8÷1/4.`

`⇒x=9/8. 4/1.`

`⇒x=9/2.`

`b)(2x+1)^3=-8.`

`⇒(2x+1)^3=(-2)^3.`

`⇒2x+1=-2.`

`⇒2x=-2-1.`

`⇒2x=-3.`

`⇒x=-3/2.`

`c)(2x-1)^2=9/16.`

`⇒(2x-1)^2=(3/4)^2=(-3/4)^2.`

`⇒2x-1=3/4.\text{ hoặc }2x-1=-3/4.`

$\text{* Trường hợp 1:}$ `2x-1=3/4.`

`⇒2x=3/4+1.`

`⇒2x=3/4+4/4.`

`⇒2x=7/4.`

`⇒x=7/4÷2.`

`⇒x=7/4. 1/2.`

`⇒x=7/8.`

$\text{* Trường hợp 2:}$ `2x-1=-3/4.`

`⇒2x=-3/4+1.`

`⇒2x=-3/4+4/4.`

`⇒2x=1/4.`

`⇒x=1/4÷2.`

`⇒x=1/4. 1/2.`

`⇒x=1/8.`

$\text{Vậy x = $\dfrac{7}{8}$ hoặc x = $\dfrac{1}{8}$.}$