推 a159371153 : 感謝! 04/01 01:47
※ 引述《a159371153 (小白)》之銘言:
: https://i.imgur.com/0SmZM79.jpg
: 我算得超級複雜,有沒有更好的算法?
: 而且答案只有根號15而已
|a - 2b| = 2(a - 2b) * b = 2(a * b) - 16
|a - 2b|^2 = 56 - 4(a * b)
= (2(a - 2b) * b)^2
= 4[(a * b) - 8]^2
=> (a * b)^2 - 15(a * b) + 50 = 0
=> a * b = 5, 10
但是|a - 2b| >= 0 => a * b >= 8
所以a * b = 10 => |a - 2b| = 4
△ = (1/2) * 2 * 4 * (1/4) √15 = √15
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