PCDVD數位科技討論區 - 瀏覽單個文章 - 想請問一題微積分的問題如何解

引用:

Originally posted by Cudacke
1/L1 = cos(x)
8/L2 = sin(x)

=> L1 + L2 = 1/cos(x) + 8/sin(x)
d(L1 + L2)/dx = sin(x)/(cos(x)^2) - 8cos(x)/(sin(x)^2)

let d(L1 + L2)/dx = 0
=> sin(x)/(cos(x)^2) = 8cos(x)/(sin(x)^2)
=> sin(x)^3 = 8*cos(x)^3
=> sin(x) = 2cos(x)
=> tan(x) = 2
=> L1 = sqrt(1^2 + 2^2) = sqrt(5)
=> L2 = sqrt(4^2 + 8^2) = sqrt(80)

Proofs of Derivative of Trig Functions

有人求出來了，這位大大真利害，微分兩次原來是求反曲點，只要微一次就好了。
我還是繼續看照片好了。