What is x given that `log_4 (x-5)=-1`

7 Answers | Add Yours

baxthum8's profile pic

baxthum8 | High School Teacher | (Level 3) Associate Educator

Posted on

What is x given `log_(4)(x-5)=-1`

`Log Rule:   `

`log_(x)a = brArr x^b = a`

` 4^-1 = x - 5`

` 1/4 = x - 5 `

`1/4 + 5 = x`

`1/4 + 20/4 = x`

`21/4 = x `

``

justaguide's profile pic

justaguide | College Teacher | (Level 2) Distinguished Educator

Posted on

The value of x has to be determined given that `log_4(x - 5) = -1`

`log_4(x - 5) = -1`

If  `log_a x = b` , `x = a^b`

` `=> `x - 5 = 4^-1`

=> `x = 1/4 + 5`

=> `x = 5.25`

The required value of x is 5.25

Jyotsana's profile pic

Jyotsana | Student, Grade 10 | (Level 1) Valedictorian

Posted on

Log4(X-5) =-1

LogCD= a ----- ca= D

X-5=4-1

X-5= 0.25    Add 5 to the both side.

 x-5+5=0.25+5

X=5.25

chhavy's profile pic

chhavy | (Level 1) eNoter

Posted on

Equation: `log_(4)(x-5) = -1`

To find: value of x

Answer: we will use the following properties:

  1. `x^(-1)=1/x` 
  2. `log_(a)(x)=y``=> x = a^y`

 now from the given equation

`log_(4)(x-5) = -1`

`=> (x-5) = 4^-1`

`=> x-5 = 1/4`

`=> x = 5+(1/4)`

`=> x = 5 + 0.25`

`=> x = 5.25`

` `

Wiggin42's profile pic

Wiggin42 | Student, Undergraduate | (Level 2) Valedictorian

Posted on

To get rid of the log, we must do the opposite function which is an exponent. Make both sides an exponent with a base for 4. this gets you

x - 5 = 4^-1 = 1/4

Now, you can solve for x just like any other linear function: 

x = .25 + 5

x = 5.25

We’ve answered 318,916 questions. We can answer yours, too.

Ask a question