Question

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

Answer 1

Answer:

Option D.

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

Step-by-step explanation:

Given the following equation:

$\frac{1}{2}(2x + 4) = 3x-c$

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

$\frac{1}{2}(2(4) + 4) = 3(4)-c$

Now you need to solve for "c":

$\frac{1}{2}(8 + 4) = 12-c\\\\\frac{12}{2}= 12-c\\\\6=12-c\\\\c+6=12\\\\c=12-6\\\\c=6$

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":

$\frac{1}{2}(2x + 4) = 3x-(4)\\\\x+2=3x-4\\\\2+4=3x-x\\\\6=2x\\\\\frac{6}{2}=x\\\\x=3$