X
1. 2x^2 - 8 = 2(x^2 - 4) = 2(x+2)(x-2)
2. 2x^2 + 8x + 6 = 2(x^2 + 4x + 3) = 2(x+3)(x+1)
3. 3n^2 + 9n -30 = 3(n^2 + 3n - 10) = 3(n+5)(n-2)
XII
1. x^2 + 2x + xy + 2y = x(x+2) + y(x+2) = (x+2)(x+y)
2. 3a^2 - 2b - 6a + ab = 3a^2 - 6a + ab - 2b = 3a(a - 2) + b(a - 2) = (a-2)(3a+b)
3. t^3 - t^2 + t - 1 = t^2(t - 1) + (t - 1) = (t-1)(t^2+1)
4. 10 + 2t - 5s - st = 10 - 5s + 2t - st = 5(2 - s) + t(2-s) = (5+t)(2-s)