※ 引述《coolching (小歐)》之銘言：
: 就算看解答也不知怎麼來的...
: 題目:
: https://i.imgur.com/jtuxnT4.jpg
: 答案:
: https://i.imgur.com/YtSg15n.jpg
: 拜託版上大大3Q
Area = (1/2)(3 + 2t)(4 + 2t)sin(Pi/2 - t)
= (1/2)[4t^2 + 14t + 12]sin(Pi/2 - t)
dArea/dt = (1/2)[8t + 14]sin(Pi/2 - t) - (1/2)[4t^2 + 14t + 2]cos(Pi/2 - t)
題目應該是問當角度為Pi/2的瞬間，t = 0時
dArea/dt值為多少
=> dArea/dt = (1/2) * 14 * 1
= 7