a, $(1-\sqrt{x})(1+\sqrt{x}+(\sqrt{x})^2)$
$=1-\sqrt{x}^3$
$=1-x\sqrt{x}$
b, $(\sqrt{x}+2)( (\sqrt{x})^2-2\sqrt{x}+2^2)$
$=\sqrt{x}^3+2^3$
$=x\sqrt{x}+8$
c, $(\sqrt{x}-\sqrt{y})( (\sqrt{x})^2+\sqrt{x}.\sqrt{y}+(\sqrt{y})^2)$
$=(\sqrt{x})^3-(\sqrt{y})^3$
$=x\sqrt{x}-y\sqrt{y}$
d,
$(x+\sqrt{y})(x^2-x.\sqrt{y}+(\sqrt{y})^2)$
$=x^3+\sqrt{y}^3$
$=x^3+y\sqrt{y}$
