Question 255006
1) y^2-49 = y^2-7^2
          = (y+7)(y-7)
2) 4x^2-25= (2x)^2-5^2
          = (2x+5)(2x-5)
3) 81x^2-1 = (9x)^2-1^2
           = (9x+1)(9x-1)