Explanation for Question 18 From the Math (No Calc) Section on the 2020 March Sat
Now question number 18 is asking us for the positive value of X that 2 satisfies this equation. And so when they say that the X satisfies 3 this equation, they're asked actually asking you to solve. 4 And if you remember, when you have a quadratic formula or something like this, 5 which is a polynomial, poly, 6 no meal, and it's set equal to zero, 7 you're basically solving for when X is equal to zero, 8 right? Or when these little sections here, 9 the little parentheses with the X, and then when those are equal to zero 10 and we do X minus three, and we set that equal to zero. 11 Then we know that this term here would be zero and multiplying it out 12 would give us the correct answer of zero. So when X minus three is 13 equal to zero, we'd be satisfying the equation because it would set the whole 14 equation equal to zero. 15 And in order to make that equal to zero, 16 I would get the X has to be equal to positive three, 17 right? But there are really two numbers where this happens where this equation is 18 true, because I can also use the other parenthesis set where X plus 19 one is equal to zero. And what I can do here is subtract one 20 from both sides. I get X minus one. 21 So all this math is showing us is that when X is positive, 22 three or X is negative one, 23 this whole equation is equal to zero, 24 which may, which means that when X is three and negative one, 25 it satisfies the equation. But we know that they're asking us for the positive 26 value of X. So we're not going to choose X being equal to negative 27 one. We have to choose three. So our best answer here is going to 28 be three.