Find the Taylor Polynomial P3(x) for f(x)=√x at 1.
Solution The first three derivatives of f(x)=√x are f′(x)=12√xf′′(x)=ddx(x−1/22)=−14x3/2f′′′(x)=ddx(−x−3/24)=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)(x−1)+f′′(1)2!(x−1)2+f′′′(1)3!(x−1)3=1+x−12−(x−1)28+(x−1)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.