Tìm x: a, (1/2)^3x-1= 1/32 b,(3/4-x)³=1/64 c, 2.3^x -405= 3^x-1

0 bình luận về “Tìm x: a, (1/2)^3x-1= 1/32 b,(3/4-x)³=1/64 c, 2.3^x -405= 3^x-1”

1. `a) (1/2)^(3x-1)=1/32`
   `⇔(1/2)^(3x-1)=(1/2)^5`
   `⇔3x-1=5`
   `⇔ 3x=5+1`
   `⇔3x=6`
   `⇔x=6:3`
   `⇔ x=2`
   Vậy `x=2`
   `b) (3/4-x)^3=1/64`
   `⇔(3/4-x)^3=(1/4)^3`
   `⇔3/4-x=1/4`
   `⇔ x=3/4-1/4`
   `⇔ x=1/2`
   Vậy `x=1/2`
   `c) 2.3^x-405=3^(x-1)`
   `⇔2.3^x-3^(x-1)=405`
   `⇔ 2.3^x-3^2. 1/3=405`
   `⇔3^x. (2-1/3)=405`
   `⇔ 3^x. 5/3=405`
   `⇔3^x=405: 5/3`
   `⇔ 3^x=243`
   `⇔ 3^x=3^5`
   `⇔ x=5`

   Vậy `x=5`

   Trả lời

2. Đáp án:

   `a) (1/2)^(3x-1)=1/32`

   `<=> (1/2)^(3x-1)=(1/2)^5`

   `<=> 3x-1=5`

   `<=> 3x=5+1`

   `<=> 3x=6`

   `<=> x=6:3`

   `<=> x=2`

   `b) (3/4-x)^3=1/64`

   `<=> (3/4-x)^3=(1/4)^3`

   `<=> 3/4-x=1/4`

   `<=> x=3/4-1/4`

   `<=> x=1/2`

   `c) 2.3^x-405=3^(x-1)`

   `<=> 2.3^x-3^(x-1)=405`

   `<=> 2.3^x-3^2. 1/3=405`

   `<=> 3^x. (2-1/3)=405`

   `<=> 3^x. 5/3=405`

   `<=> 3^x=405: 5/3`

   `<=> 3^x=243`

   `<=> 3^x=3^5`

   `<=> x=5`

   Trả lời