1)36 b^2-1-9 a^2+6a = 36b^2 - (3a -1)^2 = (6b -3a + 1)(6b + 3a -1)
2)49-25 b^2+10 a b-a^2 = 49 - (5b - a)^2 = (7 - 5b + + a)(7 + 5b - a)
3)16-25 b^2+10 a b-a^2 = 16 - (5b-a) ^2 = ( 4 - 5b + a)(4 + 5b - a)
4)25 y^2-4 x^2+12 x-9 = 25y^2 - (2x - 3) = (5y - 2x + 3)(5y + 2x - 3)