參數(shù)方程所確定的函數(shù)的二階導(dǎo)數(shù)
已知參數(shù)方程：y=f(t),x=g(t)再求y對(duì)x的二階導(dǎo)數(shù)時(shí)是這樣推導(dǎo)：
y''=[f''(t)*g'(t)-f'(t)*g''(t)]/{[g'(t)]^2}*1/g'(t)
=[f''(t)*g'(t)-f'(t)*g''(t)]/{[g'(t)]^3}
這里第一個(gè)等號(hào)的最后又乘了個(gè)1/g'(t)
是什么意思?為什么?要我自己推到就成y''=[f''(t)*g'(t)-f'(t)*g''(t)]/{[g'(t)]^2}