sininv, cosinv, taninv, sinh, cosh, tanh

1. sininv, cosinv, taninv應該即係sin, cos同tan既inverse function,即係例如當sin x = y既時候, sininv y = x.

而sinh, cosh, tanh叫做hyperbolic function. 在hyperbolic geometry入面,如果我地定義到一隻直角三角形,咁呢個直角三角形既sin, cos同tan既standard definition就係sinh, cosh, tanh.

2. Inverse function係俾左個ratio你,計返隻角出黎,定義基本上就係掉返轉頭. 而sinh x, cosh x, tanh x既定義分別係

sinh x = (e^x-e^(-x))/2
cosh x = (e^x+e^(-x)/2
tanh x = sinh x/cosh x

3. Inverse function既關係講左啦... hyperbolic function同ordinary trigo function既關係在於,其實佢地係同一類型既function,不過放左在唔同既geometry上面.

4. Inverse function既應用係俾左個trigonometric ratio,我地可以知道返隻角. 最簡單既例子係講條斜坡既斜率你知之後,你可以計返隻傾角.

Hyperbolic function既應用,三言兩語講唔到. 總之佢係hyperbolic geometry入面一個好基本既function,而hyperbolic geometry係愛因斯坦拎左去用黎解決廣義相對論入面好多計算部分既geometry啦... 咁樣講,唔知你明唔明個用途既重要性...