Interesting. I think the last expression was copied wrong, but the result is correct. I'd be happier with a method that gave an exact value (not one that you get as a decimal approximation); it might be fun to try to show that it is exactly 20.
IMG_0131.jpg
in the 3rd expression from the bottom the + should be - in front of 4sin
Last edited by yma16; 02-24-2018 at 06:49 PM.
You're my kind of person! You took the challenge.
I'm sure that work can be shortened a bit, but it's definitely a proof.
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