设|AB|=t。 角EAB为u, 角DAF为v, 阿尔法=90-(u+v)。
f(t) = u+v = arctan(1/(3*t))+arctan(t/2)
f'(t) = (15*t^2-10)/(...)
|AB|= t = sqrt(2/3) 是唯一可能。阿尔法 = 90-2*arctan(1/sqrt(6))
f(t) = u+v = arctan(1/(3*t))+arctan(t/2)
f'(t) = (15*t^2-10)/(...)
|AB|= t = sqrt(2/3) 是唯一可能。阿尔法 = 90-2*arctan(1/sqrt(6))