Find the linear approximation of f(x)=xf(x) = \sqrt{x}f(x)=x near x=4x = 4x=4 and use it to approximate 4.2\sqrt{4.2}4.2.
≈2.05\approx 2.05≈2.05
≈2.1\approx 2.1≈2.1
≈1.95\approx 1.95≈1.95
≈2.025\approx 2.025≈2.025