Explanation for Question 13 From the Math (No Calc) Section on the 2018 April Sat
Question 13 asks, which of the following could be the X coordinate of a 2 solution to the system of equations above. 3 So I'm going to start by taking this Y value negative two X plus 4 four, and plugging that into this top equation here. 5 So I'm going to rewrite this as X plus two times X 6 plus two plus negative two X 7 plus four. Plus negative three squared is equal 8 to 40. So first I'm going to factor X squared plus 9 four X plus four. And that's going to be plus negative two X plus 10 four plus negative three. 11 So that's plus one squared is equal to 40 and I can rewrite 12 that as X squared plus four X plus four times 13 two X plus one times two X plus one, 14 or sorry, negative two X plus one. And when I factored that out, 15 that becomes four plus four X squared plus 16 negative four X plus one is equal to 40. 17 Then we can add and subtract like terms. 18 So five X squared, I just took X squared and four X squared plus 19 four X plus negative four X. So those cancel out. 20 Plus five is equal to 40. 21 I can subtract five from both sides to get five X squared is 22 equal to 35, and then I can divide both sides by five to get 23 X squared is equal to seven. 24 And then finally I can square root, both sides and I get X 25 is equal to route seven or answer choice, 26 right?