Difference of two squares: Calculate or factorize: $(a+b)(a-b)=a^2-b^2$

Got it ! Simplify:

 $(x+1)(x-1) =$ $x^2 - 1^2 = x^2 - 1$ $(3x + 2y)(3x - 2y) =$ $9x^2 - 4y^2$ $(5a - 5)(3a + 3) =$ $5(a-1)3(a+1) = 15(a^2-1) = 15a^2-15$

Factorise:

 $4x^2 - 9 =$ $(2x - 3)(2x + 3)$ $121x^2 - 100y^2 =$ $(11x - 10y)(11x + 10y)$ $(a+2)^2-(a-1)^2 =$ $3(2a+1)$