Explanation for Question 15 From the Math (No Calc) Section on the 2018 May Sat
Question 15 says in the X, 2 Y plane, the points two, four, 3 and negative two negative four are the end points of a diameter of a 4 circle, which of the following is an equation of the circle. 5 So the equation of a circle is X minus H squared. 6 Plus Y minus K squared is equal to R squared. 7 So to find out what that equation is, we're going to need to know 8 what the radius is. And we're going to need to know what the central 9 point of the circle is because that's where we're getting H and K from. 10 So let's start by finding the center of the circle. 11 Well, since we know that this is an end 0.24, 12 and this is an end point, negative two, 13 negative four, we can just simply find the center of those points. 14 So the center of the X value to an X value, 15 negative two is just zero. 16 So that's the X value of the center point and the center of four 17 and negative four is also zero. 18 So we know that this circle goes through zero, 19 zero, and therefore it should be the equation should be written as X minus 20 zero squared or just X squared. 21 Plus Y minus Sierra squared or Y squared is equal to, 22 and then whatever R is squared. So from that information, 23 we can eliminate a and B already because they have different center points. 24 Now to find the radius I've quickly drawn out the circle down here, 25 which shows what the circle should look like. It has a center point of 26 zero, and these two points here, 27 negative two, negative four and two four. 28 So to f...