Question

please give the answer fast

Answer 1

20.
$27 + y^{3}$
$(3)^{3} + {(y)}^{3}$
$(3 + y) \: {(3)^2 - 3 \times y + (y)^2}$
$(3 + y) \: (9 - 3y + {y}^{2} )$

21.
$1 - 2{x}^{2}$
$(1)^{2} - ( \sqrt{2} x)^{2}$
$(1 + \sqrt{2} x)(1 - \sqrt{2} x)$