Explanation for Question 15 From the Math (Calc) Section on the Official Sat Practice Test 9
Question 15 reads line M and the X Y plane contains the points 2 two, four, and zero one, 3 which of the following is an equation of line M. 4 So the first thing we can find is we can find the slope and 5 that's done by doing Y two minus Y one over X two 6 minus X one. So let's call this X one 7 and Y one, and we can call this X two and Y 8 two. So Y two minus Y one is one minus four over 9 X, two, zero minus X, 10 one two. So we get one minus four is negative three, 11 over negative two is equal to three over two. 12 So the slope is going to be equal to three over two, 13 meaning that we can cross out points a and B. 14 The next thing is figuring out what the Y intercept is in 15 slope intercept form. We have Y equals MX plus B. 16 We found M that's the slope, and B is the Y intercept. 17 So where the graph crosses this axis right here. 18 And that could be at any point. 19 So what we're trying to find now is the Y intercept. 20 And to do that, we want to know what the Y value equals when 21 the X value is equal to zero. 22 That's the definition of the Y intercept. It's when the graph 23 crosses the Y axis right here. 24 And we're fortunate enough that that was actually one of the points given to 25 us. So we have zero one. We know that at the 0.01, 26 that's where the graph hits the Y the Y axis. 27 And we can pick our Y intercept or B to be equal to one. 28 And with that, knowing our slope intercept form, 29 we can pick answer choice D as the best answer.