Explanation for Question 28 From the Math (Calc) Section on the 2019 October Sat
Now for 28, we're told that we have a trapezoid here, 2 which has a perimeter of 20, 3 and it's made up of equal lateral triangles. 4 And so it's important to keep in mind is that if these triangles are 5 equal lateral, then each side is the same length. 6 So let's call each side X, 7 right? Let's call each of them X. 8 So we have an X here and X here and next year and next 9 year in it. And the next year now for our perimeter, 10 we can see that we're adding 1, 1, 2, 3, 4, 5 11 Xs together, right? So RP is equal to five times X. 12 Now we know our perimeter is 20 and if 20 is equal to five 13 X, then that means that each side length of X is actually four units 14 long believe in this case, it's centimeters. 15 So each side is going to be 4, 4, 4, 4, 4, 4. 16 That was whole lot long. 17 One would be eight, but we actually don't really need to know that long 18 side, because the question here is what is the area of these two triangles 19 added together? And so what can be useful here, 20 right? Is that knowing the area of a, 21 um, of a triangle, the formula for that is area is equal to base 22 times height. Now we don't have the height yet. 23 All we know is that each side length is four, but perhaps the best 24 way to go about this problem is not using that particular formula, 25 but using a different one, a different one that you might not have seen 26 before. It's a specific formula, 27 especially for an area of an equal lateral triangle. 28 So here we have area of an equa...