1) $x^{2} - 7x + 9 - 4b^{2} =$

2) $5x^{2} - 4x - 1 =$

3) $x^{4} - 7x^{2} - 8 =$

4) $1 - x^{2} + 2xy - y^{2} =$

5) $9x^{2} - 6xy + 4/9 =$

6) $x^{2} + 10x + 25 - y^{2} =$

7) $4a(x-1)^{2} - 7ax(x-1)^{2} =$

8) $x^{4} - 81 =$