Why is it 7

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[Originally posted in Discussions]
why is it 7

You're right, the 7 seems to pop out of nowhere, but it was actually covered in the Day 1: Your Turn Explanation video. Go check it out again, and see the neat trick of how the triangle with sides of 3 and 5 and middle angle of 120 degrees is turned into a right triangle simply by extending one side and dropping an altitude! It's really neat!
I hope this helps! It's good to ask questions, no matter how obvious they seem. This is called curiosity, and curiosity is good!
Happy Learning,
The Daily Challenge Team

I don't get any of this.

Hi TSS Graviser!
Are you confused about the context of the number 7 in this question? My apologies; it's hard to figure out where this came from. The 7 pops out at 1:38 in the video and is the third length of the triangle with sides of 3, 5 and 7 (with a \(120^{\circ}\) angle in between):
The explanation for why the third side of this triangle is 7 can be found around timestamp 8:00 in the Day 1: Your Turn Explanation video..
Does this answer your question? Please let us know; we're more than happy to help!
Happy Learning!
The Daily Challenge Team