我们已经看到如何约略oxima teafunct ionusingitstangentli val ueatsomepoint(sayf(a))andthevalueofthederivativeatthesame
效果好（英国《金融时报》（a）)wecanusetheseto findthetangentline,andthenusethetangentlinetoapproximatef(x)
forotherpoints x.Ofcourse thisapproximationwillonlybegoodwhenxisrelativelyneara.Thetangentlineapproximationoff(x)forxnearaiscalledthefirstdegreeTaylorPolynomialoff(x)并：
