Step 1 :\(a)\ x^2 + 12x + k = (x + a)(x + b)\)
Step 2 :\(ab = k\ and \ a + b = 12\)
Step 3 :\(k = 1 \cdot 11, 2 \cdot 6, 3 \cdot 4, -1 \cdot -11, -2 \cdot -6, -3 \cdot -4\)
Step 4 :\(k = 11, 12, 6, -11, -12, -6\)
Step 5 :\(b)\ 2x^2 + kx + 15 = (2x + a)(x + b)\)
Step 6 :\(2ab = k\ and \ a + 2b = k\)
Step 7 :\(k = 2 \cdot 1 \cdot 15, 2 \cdot 3 \cdot 5, -2 \cdot -1 \cdot -15, -2 \cdot -3 \cdot -5\)
Step 8 :\(k = 30, 30, -30, -30\)
Step 9 :\(c)\ (x - 1)^2 - k = (x - a)(x - b)\)
Step 10 :\((a - 1)(b - 1) = k\ and \ a + b = 2\)
Step 11 :\(k = 1 \cdot 1, -1 \cdot 3, -3 \cdot 5, -5 \cdot 7\)
Step 12 :\(k = 1, -3, -15, -35\)
Step 13 :\boxed{a: \{11, 12, 6, -11, -12, -6\}, b: \{30, -30\}, c: \{1, -3, -15, -35\}}\)