Explanation for Question 16 From the Math (No Calc) Section on the 2017 May Sat
Question 16 reads and the equation a equals X minus four, 2 and B equals X plus four. 3 And B are constants. When the product a B is written in the form, 4 X squared minus C, we're seeing is a constant, 5 what is the value of C? So there's two parts to this question. 6 The first part is talking about the product of a B. 7 And then the second part is asking about how to find C or the, 8 the constant in this case. So let's first find the product of AB you 9 should know, product just means multiplication. So we're just going to read multiplying a 10 times B, we know what a is because a is X minus 11 four. They tell us that, and we know a, 12 B is B as X plus four. 13 So we set up our parentheses sets like this, 14 and now we go ahead and multiply. 15 So multiply this. We have to foil. So we do first times first, 16 which is X squared, outer times outer, 17 which is four X enter times enter, 18 which is negative four X. And then last times loss, 19 which gives us negative 16. Now we don't 20 have it in X squared minus C form just yet. 21 But if we do some simplification, we'll get there. 22 So if we go through this and we'll combine like terms, 23 the four X negative four extras cancel out and we're just left with X 24 squared minus 16. Now we can see that this isn't the same format 25 as this X squared minus C. And all they want to know is what 26 C is. So our answer is 16. 27 Uh, easy mistake right here would be to say, it's negative 16. 28 It's not because they already included the negative here. 29 So you're only looking at this variable, 30 which is 16 or this constant, which is 16.