Answer Choices
8
0
−1
−8
Explanation for Question 10 From the Math (No Calc) Section on the Official Sat Practice Test 1
So number 10 gives us the function G and it tells us that a 2 is a constant and GFR is equal to eight. 3 And then they want us to find the value of G of negative four. 4 So when we see this, we know that we want to plug negative four 5 into our equation. So we would write G of negative four is equal to 6 a times X squared plus 24. 7 And then if you did that, you would be stuck here, right? 8 Because we have this value of a, that we don't know. 9 And in order to solve this equation, we need to know what a is. 10 And so that's why they've given us this, because now they've given us the 11 Y value and they've given us the X value and we can actually use 12 those to solve for a, so let's rewrite this equation here G of four 13 is equal to a times four squared plus 24. 14 And we know what G of four is it's eight, 15 right? So I can plug that in here. Eight is equal to a times 16 four squared plus 24. Now my only variable here is actually a 17 and I can solve for a and use that later on. 18 So I've got eight is equal to a times 16 plus 24. 19 I'll start by subtracting 24. That does not look like a two. 20 There we go. And when I do that, 21 I will get negative. 16 is equal to 16, 22 and then I get a, is equal to negative one. 23 Now make sure that you don't pick negative. One is your answer, 24 right? We don't know that negative one is our answer. 25 We know that a is equal to negative one. So now I can go 26 back here where I started. And instead of having a question mark for what 27 AA is, I can use negative one. So G of negative four will be 28 equal to negative X squared plus 24 now 29 negative four, right? So negative, 30 negative four squared plus 24 negative four squared is going to be 16. 31 So I have negative 16 because of this negative sign right here, 32 plus 24. And that'll give me eight. 33 So our best answer for 10 is going to be a.