.

(2)(4x-3y)^2- 16y^2

=(4x-3y+4y)(4x-3y-4y)

=(4x+y)(4x-7y)

.

(3)8 1(a-b)^2- 16(a+b)^2

=[9(a-b)+4(a+b)]*[9(a-b)-4(a+b)]

=( 13a-5b)(5a- 13b)

.

Suppose a+b = 3 and a-b =- 1/3, then:

a^2-b^2=(a+b)*(a-b)=3*(- 1/3)=- 1