※ 引述《lilygarfield (好想有個女朋友喔)》之銘言：
: 已知函數 y = f(x), 有反函數 f^(-1)(x)
: 將 y = f(x) 的圖象繞 (1,-1) 逆時鐘旋轉 90度後
: 所得的曲線方程式為何？
y = f(x) 上一點 (x0,y0)
旋轉後的位置為 (x',y') = (1-(y0+1),-1+(x0-1)) = (-y0,x0-2)
又 x0,y0 滿足 y = f(x) 即 y0 = f(x0)
代入 x' = -y0, y' = x0-2 可得
-x' = f(y'+2)
-1
即 y' = f (-x') - 2
把 ' 拿掉即為所求
--
'You've sort of made up for it tonight,' said Harry. 'Getting the
sword. Finishing the Horcrux. Saving my life.'
'That makes me sound a lot cooler then I was,' Ron mumbled.
'Stuff like that always sounds cooler then it really was,' said
Harry. 'I've been trying to tell you that for years.'
-- Harry Potter and the Deathly Hollows, P.308
--
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