The linear approximation of a function [tex]f(x)[/tex] centered at [tex]x=a[/tex] is
[tex]L(x)=f(a)+f'(a)(x-a)[/tex]
We have
[tex]f(x)=x^2\implies f'(x)=2x[/tex]
and we want to find [tex]L(10.1)[/tex] for [tex]a=10[/tex].
Since [tex]f(10)=100[/tex] and [tex]f'(10)=20[/tex], we get
[tex]10.1^2\approx L(10.1)=100+20(10.1-10)=102[/tex]
Compare this to the actual value of [tex]10.1^2=102.01[/tex].