Question

In the equation below, for what value of c does x = 4?
1 / (2x + 4) = 3x-c

Answer 1

Option D.

Jenn's answer is not correct. She got it substituting
`c=4` into the equation and solving for "x".

Explanation:

Given the following equation:

`(1)/(2)(2x + 4) = 3x-c`

Since you need that
`x=4`, you hace to substitute that value into the equation:

`(1)/(2)(2(4) + 4) = 3(4)-c`

Now you need to solve for "c":

`(1)/(2)(8 + 4) = 12-c\\\\(12)/(2)= 12-c\\\\6=12-c\\\\c+6=12\\\\c=12-6\\\\c=6`

Therefore for a a value of
`c=6`, you get
`x=4`

Then, the you can identify that the correct answer is the one given in the Option D.

Jenn made a mistake, because she substituted
`c=4` into the equation and then solve for "x":

`(1)/(2)(2x + 4) = 3x-(4)\\\\x+2=3x-4\\\\2+4=3x-x\\\\6=2x\\\\(6)/(2)=x\\\\x=3`