Explanation for Question 21 From the Math (Calc) Section on the 2020 March Sat
So now we're looking at question number 21, which says that the equation of 2 a graph shown is a X plus B Y is equal to six or 3 a, and B your constants. And we want to know what is the value 4 of B? So this equation of the line, 5 a X plus B Y is equal to six, 6 is what we would call a standard form. And typically when we write a 7 line, our inclination is to write it in Y intercept form, 8 which looks like this, Y equals MX plus B. 9 So what we can do is take this graph, 10 right? And Y intercept form, and then we'll be able to change it. 11 So that from Y intercept form, we've now written it into standard form. 12 So we'll start here and then we'll work our way to this form. 13 So, first thing we need to know is B right? 14 What is our Y intercept? And that happens where we cross the Y axis, 15 which is a negative two. So as we start writing our equation, 16 it'll be Y equals MX minus two. 17 And now we need to find the slope and to do this graphically. 18 I first need to find where two points are on the graph. 19 You can always use the y-intercept and then it looks like there's another point 20 right here. And so to find the slope, I'll just do rise over run, 21 right? So I went up one up one and over three. 22 So I have a slope of positive one-third. So I can rewrite this as 23 one-third X minus two. And now my goal that now that I'm in Y 24 intercept form is to get into standard form. 25 And I can do that by moving this X to the other side of 26 the equation. First, whe...