m^2-9n^2=m^2-(3n)^2=(m+3n)(m-3n)

0.25x^2-8 1y^2=(0.5x)^2-(9y)^2=(0.5+9y)(0.5-9y)

9a^2-b^2y^2=(3a)^2-(by)^2=(3a+by)(3a-by)

(x+5)^2-4=(x+5)^2-2^2=(x+5+2)(x+5-2)=(x+7)(x+3)

(a+b)^2-a^2=(a+b-a)(a+b+a)=b(2a+b)

49(a-b)^2- 16(a+b)^2=[7(a-b)]^2-[4(a+b)]^2=[7(a-b)+4(a+b)][7(a-b)-4(a+b)]=(7a-7b+4a+4b)(7a-

7 b-4a-4b)=( 1 1a-3b)(3a- 1 1b)

(a^2+b^2)^2-a^2b^2=(a^2+b^2)^2-(2ab)^2=(a^2+b^2+2ab )(a^2+b^2-2ab)=(a+b)^2(a-b)^2