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EXAMPLE 1Finding a Taylor Polynomial for f(x)=x

Find the Taylor Polynomial P3(x) for f(x)=x at 1.

Solution The first three derivatives of f(x)=x are f(x)=12xf(x)=ddx(x1/22)=14x3/2f(x)=ddx(x3/24)=38x5/2

Then f(1)=1f(1)=12f(1)=14f(1)=38

The Taylor Polynomial P3(x) for f(x)=x at 1 is P3(x)=f(1)+f(1)(x1)+f(1)2!(x1)2+f(1)3!(x1)3=1+x12(x1)28+(x1)316

The graphs of the function f and the Taylor Polynomial P3 are shown in Figure 17. Notice how P3(x)f(x) for values of x near 1.