-9x^2+1 can be rearanged into 1-9x^2 look familiar? 1^2-(3x)^2 (1-3x)(1+3x) or (1-3x)(3x+1) we nowhave (3x+1)(5x-4)-(x-12)(3x+1)+(1-3x)(3x+1) factor out (3x+1) (3x+1)(5x-4-(x-12)+1-3x) (3x+1)(2x-3-x+12) (3x+1)(x+9)
b. easy
a^2-b^2=(a-b)(a+b) (4x+5)^2-(2x-3)^2= (4x+5-(2x-3))(4x+5+2x-3)= (4x+5-2x+3)(6x+2)= (2x+8)(6x+2) we can factor out the 2 from each (4)(x+2)(3x+1)
