<p>The problem appeared really intimidating to me when I first saw it, but it doesn’t seem that hard now. For now, I only proved part 1 because it’s so late. I refreshed my math mind for the time being. Good prep for going to college next year.</p>
<p>Some Paper 2 IB HL math problems on the exam are much harder than this one. I agree with the above posters that this isn’t necessarily a good representation. The Chinese problem should be compared to an AP Free Response, IB HL Paper 2, or A-level problem (not familiar with the exam), not a 3-4-5 triangle. The difficulty is about the same, given similar time constraints.</p>
<p>Spoiler Warning:</p>
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<li>Set D to coordinate (0,0,0). Let AD be the x axis and CD be the y axis. Thus, we can find the points A, C, and D since they gave the magnitudes. We know the z coordinate for B is 0, so we need to find the x and y coordinates for B, which we define as Bx and By. We have two givens: 1. Magnitude of AB is 2, so we can use Pythagorean theorem to write one equation with 2 unknowns. 2. Line AC is perpendicular to Line BD. Since D is the origin, BD is the same as B. We can write another equation with the scalar product of AC and BD. Two equations, two unknowns, and we can find Bx, By, and the coordinate B.</li>
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<p>We use the scalar product again to find the proof for the perpendicular BD and A1C. We already found BD, and A1 is just A except with a Z coordinate of Sqrt(3) instead of 0. Find the vector A1C, and then scalar product the two vectors (BD and A1C). The scalar product is 0, proving that it’s perpendicular.</p>
<ol>
<li><p>We know the coordinates for A1, B, and D. We also know C1 is just C with a z coordinate of Sqrt(3) instead of 0. Find position vectors from B to A1 and B to D, and take the cross product. Find vector from BC1 and BD and take the cross product. Use the scalar product formula (a*b = [a]**cosn), where [a] is the magnitude of a. Thus find n, the angle.</p></li>
<li><p>We know A, we know D, we know B, we know C1. Find vectors AD and BC1. Use the scalar product formula to find the angle.</p></li>
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<p>Sorry, I got too excited when doing this problem. I should have entered the contest :(</p>