Explanation for Question 22 From the Math (Calc) Section on the 2020 October Sat
So for thinking about question 22 is asking us to write a, 2 a very general function that describes the parabola. 3 The easiest thing to notice about this parabola is that it's pointing downwards. 4 And if a parabola is pointing downwards, it needs to have a negative sign 5 out in front of the H value since B, 6 C, and D only have positive a values, 7 they can't be right. So now we're choosing between a and B because they 8 both have the negative. We can see now that the second difference between a 9 and B I guess the only difference between a and B. 10 But the second thing we're going to look at is whether or not the 11 B has a negative sign in front of it or a positive sign in 12 front of it. And we can remember that the B value corresponds to the 13 X value of the vertex. 14 And if we look at where our vertex is, we can see that our 15 vertex has a positive X, 16 right? Because I've moved this way from the origin. 17 And now this part gets a little tricky, right? Because when we're working with 18 parabolas inside of these parentheses, 19 you actually use the opposite sign of where the number actually goes. 20 So since this is a positive X, 21 that means we actually need a negative B. 22 Since we need a negative B answer choice B is no good. 23 And so that leaves us with a.