factor

1. a^2 - 5a - 6

2. b^2 - 7b + 12

3. 3x^2 + 2xy - y^2

4. 3y^4 - 2y^2 - 5

5. a^2b^2 - 7ab + 10

6. y^2 - xy - 56x^2

7. 4x^2+ 8xy - 60y^2