2.x 2-3x- 1 = 0, then x 1+x2=-b/a=3.

3.MX 2-4x-4 = 0 has a real number root, △≥0, that is, 16-4mx(-4)≥0, that is, 16+ 16m≥0, that is, m≥- 1.

5. Because the two waists are equal, then △=0, which is B? -4ac=0 means 16-4k=0, then k=4.