All of these make use of the expansion
(a + b)² = a² + 2ab + b²
You would do well to memorize this "formula." Of course, it also helps to be able to double (or halve) a number, and to know the squares of small integers.
1.
x² +2x +1
x² -6x +9
x² +12x +36
x² -0.4x +0.04
4x² +28x +49
9x² +30x +25
2.
(x + 4)²
(x + 3)²
(x - 9)²
(x - 5)²
3. (12/2)² = 36
4. ±2√49 = ±14
