Precalculus (6th Edition) Blitzer

Step 1. Set values of $x$ approaching $4$ from both sides; for example $x=3.9, 3.99, 3.999, 4.1, 4.01, 4.001$ Step 2. Evaluate the function value $f(x)=x^2$ at each point and put the data in a table. Step 3. Examine the trend of the function value when $x\to4$ to get $\lim_{x\to4}x^2=16$