Explanation for Question 23 From the Math (Calc) Section on the 2019 April Sat
For number 23, we are given this figure here where ACD is a right 2 triangle and B. He is parallel to C D and 3 we want to find the perimeter of ACD to the nearest 10th of a 4 unit. So because these two lines are parallel that makes 5 them similar triangles, and that makes it a lot easier for us to find 6 our missing sides. So the only reason we can use this method is because 7 of this part right here, where it says that B E is parallel to 8 C D in order for two triangles to be similar, 9 they have to have the same interior angles. 10 And because they have the same angles, 11 we can then use a constant ratio between the sides. 12 So if these lines are parallel, 13 those two angles are equal. Along with these two, 14 they're both red angles. And then since this angle is shared between both triangles, 15 it is the same. 16 So we are good to go on using them. We can compare the ratios 17 of the sides now. So the ratio of this side to this side is 18 going to equal the ratio of this side, 19 to this side in the big triangle. 20 So if we set that up five, 21 over three is going to equal AC the missing 22 side overnight. 23 I did the vertical side over the horizontal side, 24 equals the vertical side over the horizontal side for both triangles. 25 So now you can either cross multiply to find AC, 26 or you can see that there's a constant factor that it's increasing by. 27 So this three is multiplied by three to get nine. 28 So five is going to be multiplied by three to get this whol...