Answer Choices
−3
−2
0
2
Explanation for Question 14 From the Math (Calc) Section on the Official Sat Practice Test 8
So question 14 asks us, which of the following is a value of X 2 for which this expression is undefined. 3 And so we have to think to ourselves, what will make an expression? 4 Undefined? What am I looking for here? And the key to this is 5 in the denominator, because if you want to try this out, 6 you can put anything in your, in your calculator, 7 right? Any number divided by zero doesn't matter. 8 And it will tell you on the find, 9 it'll tell you it's an air. And the reason it's an error is because 10 you can't divide things by zero. So for looking for something that's undefined, 11 we're trying to find X where that value of X makes our denominator 12 equal to zero. And so the way that we do this is by factoring 13 this equation, that way we can solve for X. 14 So we have X squared, plus three X minus 10. 15 We see that we just have a normal X squared at the front of 16 this, right? There's no coefficient on the X. 17 So we can set up our factoring as two sets of parentheses with exit 18 the front. And now we know that we want to choose a numb or 19 two, two numbers that will multiply to give us negative 10 and add to 20 give us positive three. So we can think about using five and two. 21 And if I want a positive three, I can make that two negative because 22 five times negative two is negative 10 and five minus two is positive three. 23 So now I can just put those in my parentheses and I can set 24 them equal to zero. And if I subtract 25 five from both sides here, I get the X is equal to negative five. 26 And if I add two to both sides here, I get the X is 27 equal to two. And so I see that I have D X is equal 28 to X equals negative five. Isn't on there. 29 It's not an answer choice, but that doesn't mean it's wrong. It's just not 30 an answer choice here. And so our best answer is going to be D.