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  • A shooting star crashes on Earth, and a hideous blob emerges.

  • It creeps and leaps, it glides and slides.

  • It’s also unstoppable: weapons, fire, extreme temperaturesno matter what you throw at it, it just regrows and continues its rampage.

  • Its expansion is breathtaking; it doubles in size every hour.

  • But there’s one opportunity: after each hour, it goes to sleep, forming itself into a flat triangle and resting for a few minutes before it begins eating and growing again.

  • Your only chance to save the planet involves a satellite-mounted nano-fission ray that can cut through the blob.

  • When the blog is active it heals itself within seconds.

  • However, when you break the sleeping blob into two triangles, you make a critical discovery.

  • The acute triangle portion, with all angles less than 90 degrees, is inert.

  • It neverwakes up.”

  • The obtuse triangle, which has an angle greater than 90 degrees, wakes up as usual and keeps growing.

  • Similar experiments show that all shapes other than acute triangles, including right triangles, will also wake up.

  • For the next few minutes, the blob is sleeping in its obtuse triangle form.

  • You can make clean, straight-line cuts between any two points on or inside the triangle.

  • But youll only have time to make 7 cuts while the satellite is above you.

  • By the time it completes its orbit and returns, the blob will have consumed the entire world, if even a single portion that will wake up remains.

  • How can you cut the blob entirely into acute triangles and stop it from destroying the planet?

  • Pause the video now to figure out for yourself

  • Answer in 3, 2 ,1.

  • While this seems doable at first, there’s a hidden difficulty when it comes to avoiding obtuse and right angles.

  • Every time you make a cut that reaches an edge, it either makes an acute and an obtuse angle, or two right angles.

  • That makes it seems like youre doomed to keep creating obtuse angles.

  • But as with so many of life’s problems, we can look to pizza for inspiration.

  • Imagine squaring off the outside of a pizza, so that instead of a circle, it’s an octagon.

  • When we cut it into slices, each of the eight triangles is acute.

  • This works with larger polygons too.

  • Importantly, it also works for some polygons with fewer sides, including heptagons, hexagons, and pentagons.

  • That’s good news, because if you cut off the sharp corners of the blob triangle, a pentagon is exactly what youll be left with.

  • And just like a pizza, you can cut the blob pentagon into 5 acute triangles.

  • That’s 7 cuts, and it renders the blob completely inert.

  • Youve saved the day!

  • Now you just need to figure out what to do with all of these giant, practically indestructible triangles.

  • Here is a bonus riddle for you: are triangles the best shape?

  • Just kidding, that's not a riddlebut it is worth discussing! Watch these lessons and decide for yourself.

A shooting star crashes on Earth, and a hideous blob emerges.


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C1 上級

止められないブロブの謎を解くことができるか?- ダン・フィンケル (Can you solve the unstoppable blob riddle? - Dan Finkel)

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    林宜悉 に公開 2021 年 01 月 14 日