Answer:
By multiplying the term by itself (x+1)(x+1)
Some people like to use the box technique, which formats like this:
x + 1
x x^2 1x
+
1 1x 1
The terms multiply in columns, and then add all together
So
x^2 + 1x + 1x + 1 can be simplified to x^2+2x+1 = 0, which is the perfect square of (x+1)^2 = 0
Explanation: