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) = $	$9x^2 - 4y^2$
$(5a - 5)(3a + 3) =$	$\LARGE 5(a-1)3(a+1) = 15(a^2-1) = 15a^2-15 $
$(a - 1)(a + 1)(a^2 + 1)) =$	$\LARGE (a^2-1)(a^2+1) = a^4 - 1 $
$x^{20} - (x^{10} - 1)(x^{10} + 1) =$	$\LARGE x^{20} - (x^{20} - 1) = 1$

Factorise:

$4x^2 - 9 = $	$(2x - 3)(2x + 3)$
$121x^2 - 100y^2 = $	$(11x - 10y)(11x + 10y)$
$(a+2)^2-(a-1)^2 =$	$\LARGE 3(2a+1) $
$a^3-(a-1)^2a =$	$\LARGE a[a^2-(a-1)^2] = a(2a - 1)1 = a(2a - 1)$
$18-2(a-1)^2 =$	$\LARGE 2[9-(a-1)^2] = 2(4 - a)(2 + a) $