老媽問英文
Fun with maths: prove Cos pi/7 + cos 3pi/7 + cos 5pi/7=1/2媽:「兒子、兒子!來!『It's too easy!』是啥?」兒子:「『這! 太簡單了』。」媽媽:「簡單還不快說?」兒子:「啊就是『太簡單了』呀!」媽媽:「你以為我不敢揍你嗎?」語畢,就將兒子教訓了一頓。接著,媽媽又問:「『what』這字何解?」兒子:「『什麼』。」媽媽:「我說:『what』是啥意思To prove Cos pi/7 + cos 3pi/7 + cos 5pi/7=1/2 let z = cos pi/7 + i sin pi/7 z^7 = cos pi + i sin pi = - 1 so z^7+1 = 0 (z+1) (z^6-z^5+z^4 - z^3+z^2 -z + 1) = 0 as z is not - 1 so z^6-z^5+z^4 - z^3+z^2 -z + 1 = 0 so z^6-z^5+z^4 - z^3+z^2 -z= -1 so z+z^3+ z...
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