This type of question always messes up my students. At the heart of this question is a fact you should memorize: When you see the word "undefined" in a math problem, there is a basic definition or fact that is in play. You can't divide by zero. That's a fact. So, since the denominator of a fraction is the way we divide (called the divisor) then you can never have zero in the denominator of a fraction and have it work! WHEN there is a zero in the denominator, we call that expression "undefined". (Hopefully you also know that the denominator is the BOTTOM of the fraction.
So in this problem, you just have to figure out what value would make the denominator zero, which in turn will make the whole fraction "undefined".
12x / 5+x was original equation given. To solve for when it is undefined, set the denominator equal to zero:
5 + x = 0 Now solve: 5 plus WHAT = 0? 5 + -5 = 0! So the answer is (A) -5
Helping GED candidates pass their tests is one of my absolute favorite things to do. I have two students that have passed this month!