Simplify: (x + y)3 - (x - y)3 - 6y(x2 - y2)
(3x - 5y - 4) (9x2 + 25y2 + 15xy + 12x - 20y + 16)= {(3x) + (-5y) + (-4)} {(3x)2 + (-5y)2 + (-4)2 - (3x) (-5y) - (-5y) (-4) - (-4) (3x)}= (3x)3 + (-5y)3 + (-4)3 - 3 (3x) (-5y) (-4)= 27x3 - 125y3 - 64 - 180cy.
Factorise each of the following:
a4 - b4 (b)a4 - 16b4
a4 - 16b4
a2 - (b - c)2